[ccp4bb] AW: [ccp4bb] twinning fun
Dear Bert, The first thing I would do is to calculate the Matthews number: Does at least one monomer fit in the P622 asymmetric unit? If not, your crystals are definitively twinned. As mentioned below, I would also check the I^2/I^2 ratio, but I would do it with the data processed in P6, since processing true P6 data in P622 will produce a twinned ratio even when the P6 data was not twinned. If it turns out, that some crystals are twinned and others not, I would look at the diffraction patterns to see if something funny is going on (ice rings, high background, strange spot shape etc.). In this case, I would try to solve the structure with untwinned crystals. Maybe less fun, but also less hassle, frustration and cleaner maps. Best, Herman Von: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] Im Auftrag von Dirk Kostrewa Gesendet: Dienstag, 28. Januar 2014 22:01 An: CCP4BB@JISCMAIL.AC.UK Betreff: Re: [ccp4bb] twinning fun Dear Bert Van-Den-Berg, as far as I understand this, if you have true P622, process the data in P6 and then test for twinning, both the Britton-test and H-test will indicate perfect merohedral twinning. This is because the Britton-test checks for a sudden increase of negative intensities after de-twinning, which happens only at twin fractions close to 0.5 if the intensities used for de-twinning are the same. But this is true if they are related by crystallographic symmetry. The H-test relates the absolute difference to the sum of the presumably twinned intensities, which gives 0 for intensities related by crystallographic symmetry, again resulting in twin fractions close to 0.5. In other words, intensities related by crystallographic symmetry would indicate perfect twinning in both of these tests. A better test for perfect merohedral twinning would be the ratio of I^2/I^2 which should be 2 for untwinned and 1.5 for perfectly twinned data, tested in the higher space group. These values are reported by data processing programs like XDS. Please, be aware that these ratios have rather strange values if you have an unusually high background (loop fiber diffraction, ice rings, etc.) or extremely weak data. For a really good discussion of twin tests, see Yeates, Methods. Enzymol. 276, 344-358, 1997. Best regards, Dirk. Am 28.01.14 18:26, schrieb Bert Van-Den-Berg: Dear all, I recently collected several datasets for a protein that needs experimental phasing. The crystals are hexagonal plates, and (automatic) data processing suggests with high confidence that the space group is P622. This is where the fun begins. For some datasets (processed in P622), the intensity distributions are normal, and the L-test (aimless, xtriage) and Z-scores (xtriage) suggest that there is no twinning (twinning fractions 0.05). However, for other datasets (same cell dimensions), the intensity distributions are not normal (eg Z-scores 10). Given that twinning is not possible in P622, this suggests to me that the real space group could be P6 with (near) perfect twinning. If I now process the normal L-test P622 datasets in P6, the twin-law based tests (britton and H-test in xtriage) give high twin fractions (0.45- 0.5), suggesting all my data is twinned. Does this make sense (ie can one have twinning with normal intensity distributions)? If it does, would the normal L-test datasets have a higher probability of being solvable? Is there any strategy for experimental phasing of (near) perfect twins? SAD would be more suitable than SIR/MIR? (I also have potential heavy atom derivatives). Thanks for any insights! Bert -- *** Dirk Kostrewa Gene Center Munich, A5.07 Department of Biochemistry Ludwig-Maximilians-Universität München Feodor-Lynen-Str. 25 D-81377 Munich Germany Phone: +49-89-2180-76845 Fax: +49-89-2180-76999 E-mail: kostr...@genzentrum.lmu.demailto:kostr...@genzentrum.lmu.de WWW: www.genzentrum.lmu.dehttp://www.genzentrum.lmu.de ***
Re: [ccp4bb] twinning fun
Dear Bert, as Dirk has pointed out, if P622 is the correct space group, then the twinning statistics printed out if you process in P6 are meaningless. Intensity statistics, like the ratio of I^2/I^2 , can be misleading if there is (e.g. pseudo-translational) NCS in the crystal; however, the effect of NCS on the value of the ratio of I^2/I^2 is opposite to that of twinning. Thus if a crystal is twinned and has NCS, you might not notice any problem in the ratio of I^2/I^2 . The other statistics, like Britton and H-test, present the intensity statistics in a different way, but from my understanding do not give substantially different information. The L-test does look at a different kind of information and therefore gives additional insight. If your measurements suffer from high background, diffuse scatter, ice rings, smeared reflections, additional crystals in the beam, or any other pathology, then all these tests may give distorted answers. In other words, even if twinning is not really present, any test designed to convert the deviation of data from ideality into an estimate of the twinning fraction will give you an alpha 0. So my experience is: if your data are very good, then the tests give good answers; if the data are mediocre or bad, don't necessarily believe the numbers. Finally, it's not only twinning of P6 that would give you P622, it's also twinning of P3x21, P3x12 that gives P6y22. Hope this helps, Kay On Tue, 28 Jan 2014 17:26:23 +, Bert Van-Den-Berg bert.van-den-b...@newcastle.ac.uk wrote: Dear all, I recently collected several datasets for a protein that needs experimental phasing. The crystals are hexagonal plates, and (automatic) data processing suggests with high confidence that the space group is P622. This is where the fun begins. For some datasets (processed in P622), the intensity distributions are normal, and the L-test (aimless, xtriage) and Z-scores (xtriage) suggest that there is no twinning (twinning fractions 0.05). However, for other datasets (same cell dimensions), the intensity distributions are not normal (eg Z-scores 10). Given that twinning is not possible in P622, this suggests to me that the real space group could be P6 with (near) perfect twinning. If I now process the normal L-test P622 datasets in P6, the twin-law based tests (britton and H-test in xtriage) give high twin fractions (0.45- 0.5), suggesting all my data is twinned. Does this make sense (ie can one have twinning with normal intensity distributions)? If it does, would the normal L-test datasets have a higher probability of being solvable? Is there any strategy for experimental phasing of (near) perfect twins? SAD would be more suitable than SIR/MIR? (I also have potential heavy atom derivatives). Thanks for any insights! Bert
Re: [ccp4bb] twinning fun
Try looking into tetartohedral twinning as well--I think I may have such a crystal, and it's tough going. And as Kay pointed out, try the various P3's. Since I have not yet been successful in figuring my similar case out, what do people on the list recommend as an approach to figuring this out--just trying every possible space group with various parameters? I would think there should be some actual advantages at the phasing step to having twins, such as a sort of NCS of intensities rather than amplitudes, weighted by twin fraction, but it doesn't seem that any software uses this. Perhaps there is a reason for that? A paper on tetartohedral twinning I saw: Acta Crystallogr D Biol Crystallogr. 2012 Apr;68(Pt 4):418-24. doi: 10.1107/S0907444912006737. Epub 2012 Mar 16. Tetartohedral twinning could happen to you too. Roversi P, Blanc E, Johnson S, Lea SM. Author information Abstract Tetartohedral crystal twinning is discussed as a particular case of (pseudo)merohedral twinning when the number of twinned domains is four. Tetartohedrally twinned crystals often possess pseudosymmetry, with the rotational part of the pseudosymmetry operators coinciding with the twinning operators. Tetartohedrally twinned structures from the literature are reviewed and the recent structure determination of tetartohedrally twinned triclinic crystals of human complement factor I is discussed. PMID: 22505261 [PubMed - indexed for MEDLINE] PMCID: PMC3322600 Free PMC Article JPK -Original Message- From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Kay Diederichs Sent: Wednesday, January 29, 2014 4:17 AM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] twinning fun Dear Bert, as Dirk has pointed out, if P622 is the correct space group, then the twinning statistics printed out if you process in P6 are meaningless. Intensity statistics, like the ratio of I^2/I^2 , can be misleading if there is (e.g. pseudo-translational) NCS in the crystal; however, the effect of NCS on the value of the ratio of I^2/I^2 is opposite to that of twinning. Thus if a crystal is twinned and has NCS, you might not notice any problem in the ratio of I^2/I^2 . The other statistics, like Britton and H-test, present the intensity statistics in a different way, but from my understanding do not give substantially different information. The L-test does look at a different kind of information and therefore gives additional insight. If your measurements suffer from high background, diffuse scatter, ice rings, smeared reflections, additional crystals in the beam, or any other pathology, then all these tests may give distorted answers. In other words, even if twinning is not really present, any test designed to convert the deviation of data from ideality into an estimate of the twinning fraction will give you an alpha 0. So my experience is: if your data are very good, then the tests give good answers; if the data are mediocre or bad, don't necessarily believe the numbers. Finally, it's not only twinning of P6 that would give you P622, it's also twinning of P3x21, P3x12 that gives P6y22. Hope this helps, Kay On Tue, 28 Jan 2014 17:26:23 +, Bert Van-Den-Berg bert.van-den-b...@newcastle.ac.uk wrote: Dear all, I recently collected several datasets for a protein that needs experimental phasing. The crystals are hexagonal plates, and (automatic) data processing suggests with high confidence that the space group is P622. This is where the fun begins. For some datasets (processed in P622), the intensity distributions are normal, and the L-test (aimless, xtriage) and Z-scores (xtriage) suggest that there is no twinning (twinning fractions 0.05). However, for other datasets (same cell dimensions), the intensity distributions are not normal (eg Z-scores 10). Given that twinning is not possible in P622, this suggests to me that the real space group could be P6 with (near) perfect twinning. If I now process the normal L-test P622 datasets in P6, the twin-law based tests (britton and H-test in xtriage) give high twin fractions (0.45- 0.5), suggesting all my data is twinned. Does this make sense (ie can one have twinning with normal intensity distributions)? If it does, would the normal L-test datasets have a higher probability of being solvable? Is there any strategy for experimental phasing of (near) perfect twins? SAD would be more suitable than SIR/MIR? (I also have potential heavy atom derivatives). Thanks for any insights! Bert
Re: [ccp4bb] twinning fun
Dont forget that with twinning in apparent point group PG6/mmm the true SG may be P6i or P3i21 See the twinning notes: http://www.ccp4.ac.uk/dist/html/twinning.html Detecting twinning can be problematic - My rule of thumb, following the procedure od ctruncate:: 0) Check the matthews coefficient for likely number of molecules. Half a molecule must mean you are assigning too high a symmetry count. Lots of molecules means you need to check for non-crystallographic translation etc. 1) Look at the I^2/I^2 plot after correction for anisotropy If it isnt reasonably straight with resolution you probably have some data problems, and these can make all the tests pretty useless. 2) Is there a NC translation - truncate tells you that. If not, and the data is OK, you are unlikely to have twinning if I^2/I^2 for acentrics is ~ 2, and the L test looks OK. H test and Britten tests a bit more influenced by other NC symmetry considerations 3) If there IS NC translation I^2/I^2 for acentrics will probably be 2 but the L test is still pretty reliable. Good luck Eleanor experimental phasing is tricky with perfect twinning but it has been done. Sorry I have forgotten reference though.. Eleanor On 29 January 2014 09:17, Kay Diederichs kay.diederi...@uni-konstanz.de wrote: Dear Bert, as Dirk has pointed out, if P622 is the correct space group, then the twinning statistics printed out if you process in P6 are meaningless. Intensity statistics, like the ratio of I^2/I^2 , can be misleading if there is (e.g. pseudo-translational) NCS in the crystal; however, the effect of NCS on the value of the ratio of I^2/I^2 is opposite to that of twinning. Thus if a crystal is twinned and has NCS, you might not notice any problem in the ratio of I^2/I^2 . The other statistics, like Britton and H-test, present the intensity statistics in a different way, but from my understanding do not give substantially different information. The L-test does look at a different kind of information and therefore gives additional insight. If your measurements suffer from high background, diffuse scatter, ice rings, smeared reflections, additional crystals in the beam, or any other pathology, then all these tests may give distorted answers. In other words, even if twinning is not really present, any test designed to convert the deviation of data from ideality into an estimate of the twinning fraction will give you an alpha 0. So my experience is: if your data are very good, then the tests give good answers; if the data are mediocre or bad, don't necessarily believe the numbers. Finally, it's not only twinning of P6 that would give you P622, it's also twinning of P3x21, P3x12 that gives P6y22. Hope this helps, Kay On Tue, 28 Jan 2014 17:26:23 +, Bert Van-Den-Berg bert.van-den-b...@newcastle.ac.uk wrote: Dear all, I recently collected several datasets for a protein that needs experimental phasing. The crystals are hexagonal plates, and (automatic) data processing suggests with high confidence that the space group is P622. This is where the fun begins. For some datasets (processed in P622), the intensity distributions are normal, and the L-test (aimless, xtriage) and Z-scores (xtriage) suggest that there is no twinning (twinning fractions 0.05). However, for other datasets (same cell dimensions), the intensity distributions are not normal (eg Z-scores 10). Given that twinning is not possible in P622, this suggests to me that the real space group could be P6 with (near) perfect twinning. If I now process the normal L-test P622 datasets in P6, the twin-law based tests (britton and H-test in xtriage) give high twin fractions (0.45- 0.5), suggesting all my data is twinned. Does this make sense (ie can one have twinning with normal intensity distributions)? If it does, would the normal L-test datasets have a higher probability of being solvable? Is there any strategy for experimental phasing of (near) perfect twins? SAD would be more suitable than SIR/MIR? (I also have potential heavy atom derivatives). Thanks for any insights! Bert
Re: [ccp4bb] twinning fun
Also, if you have translational NCS then recent versions of Phaser can correct for the statistical effects and give you I^2/I^2 moment tests that are diagnostic of twinning. This works pretty well for 2-fold tNCS (i.e. one major Patterson peak corresponding to one or more pairs of molecules separated by the same translation). If there's higher order tNCS, then this works less well in the current version. We give some examples in the paper describing the algorithm: http://journals.iucr.org/d/issues/2013/02/00/dz5268/dz5268.pdf. Best wishes, Randy Read On 29 Jan 2014, at 13:30, Eleanor Dodson eleanor.dod...@york.ac.uk wrote: Dont forget that with twinning in apparent point group PG6/mmm the true SG may be P6i or P3i21 See the twinning notes: http://www.ccp4.ac.uk/dist/html/twinning.html Detecting twinning can be problematic - My rule of thumb, following the procedure od ctruncate:: 0) Check the matthews coefficient for likely number of molecules. Half a molecule must mean you are assigning too high a symmetry count. Lots of molecules means you need to check for non-crystallographic translation etc. 1) Look at the I^2/I^2 plot after correction for anisotropy If it isnt reasonably straight with resolution you probably have some data problems, and these can make all the tests pretty useless. 2) Is there a NC translation - truncate tells you that. If not, and the data is OK, you are unlikely to have twinning if I^2/I^2 for acentrics is ~ 2, and the L test looks OK. H test and Britten tests a bit more influenced by other NC symmetry considerations 3) If there IS NC translation I^2/I^2 for acentrics will probably be 2 but the L test is still pretty reliable. Good luck Eleanor experimental phasing is tricky with perfect twinning but it has been done. Sorry I have forgotten reference though.. Eleanor On 29 January 2014 09:17, Kay Diederichs kay.diederi...@uni-konstanz.de wrote: Dear Bert, as Dirk has pointed out, if P622 is the correct space group, then the twinning statistics printed out if you process in P6 are meaningless. Intensity statistics, like the ratio of I^2/I^2 , can be misleading if there is (e.g. pseudo-translational) NCS in the crystal; however, the effect of NCS on the value of the ratio of I^2/I^2 is opposite to that of twinning. Thus if a crystal is twinned and has NCS, you might not notice any problem in the ratio of I^2/I^2 . The other statistics, like Britton and H-test, present the intensity statistics in a different way, but from my understanding do not give substantially different information. The L-test does look at a different kind of information and therefore gives additional insight. If your measurements suffer from high background, diffuse scatter, ice rings, smeared reflections, additional crystals in the beam, or any other pathology, then all these tests may give distorted answers. In other words, even if twinning is not really present, any test designed to convert the deviation of data from ideality into an estimate of the twinning fraction will give you an alpha 0. So my experience is: if your data are very good, then the tests give good answers; if the data are mediocre or bad, don't necessarily believe the numbers. Finally, it's not only twinning of P6 that would give you P622, it's also twinning of P3x21, P3x12 that gives P6y22. Hope this helps, Kay On Tue, 28 Jan 2014 17:26:23 +, Bert Van-Den-Berg bert.van-den-b...@newcastle.ac.uk wrote: Dear all, I recently collected several datasets for a protein that needs experimental phasing. The crystals are hexagonal plates, and (automatic) data processing suggests with high confidence that the space group is P622. This is where the fun begins. For some datasets (processed in P622), the intensity distributions are normal, and the L-test (aimless, xtriage) and Z-scores (xtriage) suggest that there is no twinning (twinning fractions 0.05). However, for other datasets (same cell dimensions), the intensity distributions are not normal (eg Z-scores 10). Given that twinning is not possible in P622, this suggests to me that the real space group could be P6 with (near) perfect twinning. If I now process the normal L-test P622 datasets in P6, the twin-law based tests (britton and H-test in xtriage) give high twin fractions (0.45- 0.5), suggesting all my data is twinned. Does this make sense (ie can one have twinning with normal intensity distributions)? If it does, would the normal L-test datasets have a higher probability of being solvable? Is there any strategy for experimental phasing of (near) perfect twins? SAD would be more suitable than SIR/MIR? (I also have potential heavy atom derivatives). Thanks for any insights! Bert -- Randy J. Read Department of Haematology, University of Cambridge Cambridge Institute for Medical Research Tel: +
Re: [ccp4bb] twinning fun
Two more papers on twinning I found informative: === Acta Cryst. (2003). D59, 2004-2016[ doi:10.1107/S0907444903021085 ] Twinned crystals and anomalous phasing Z. Dauter Abstract: Merohedral or pseudomerohedral twinning of crystals cannot be identified from inspection of the diffraction patterns. Several methods for the identification of twinning and the estimation of the twin fraction are suitable for macromolecular crystals and all are based on the statistical properties of the measured diffraction intensities. If the crystal twin fraction is estimated and is not too close to 0.5, the diffraction data can be detwinned; that is, related to the individual crystal specimen. However, the detwinning procedure invariably introduces additional inaccuracies to the estimated intensities, which substantially increase when the twin fraction approaches 0.5. In some cases, a crystal structure can be solved with the original twinned data by standard techniques such as molecular replacement, multiple isomorphous replacement or multiwavelength anomalous diffraction. Test calculations on data collected from a twinned crystal of gpD, the bacteriophage [lambda] capsid protein, show that the single-wavelength anomalous diffraction (SAD) method can be used to solve its structure even if the data set corresponds to a perfectly twinned crystal with a twin fraction of 0.5. Keywords: twinning; merohedral; pseudomerohedral; anomalous scattering; SAD. === Acta Crystallogr D Biol Crystallogr. 2008 Jan;64(Pt 1):99-107. Epub 2007 Dec 5. Surprises and pitfalls arising from (pseudo)symmetry. Zwart PH, Grosse-Kunstleve RW, Lebedev AA, Murshudov GN, Adams PD. Author information Abstract It is not uncommon for protein crystals to crystallize with more than a single molecule per asymmetric unit. When more than a single molecule is present in the asymmetric unit, various pathological situations such as twinning, modulated crystals and pseudo translational or rotational symmetry can arise. The presence of pseudosymmetry can lead to uncertainties about the correct space group, especially in the presence of twinning. The background to certain common pathologies is presented and a new notation for space groups in unusual settings is introduced. The main concepts are illustrated with several examples from the literature and the Protein Data Bank. PMID: 18094473 [PubMed - indexed for MEDLINE] PMCID: PMC2394827 Free PMC Article
Re: [ccp4bb] twinning fun
Dear Bert, In my own review:- http://www.tandfonline.com/doi/abs/10.1080/08893110802360925?journalCode=gcry20#.UulGyGtYCSM molecular replacement emerged in my mind as the most robust option for structure determination in such a case, apart from finding an untwinned crystal form of course. Best wishes, John Prof John R Helliwell DSc FInstP CPhys FRSC CChem F Soc Biol. Chair School of Chemistry, University of Manchester, Athena Swan Team. http://www.chemistry.manchester.ac.uk/aboutus/athena/index.html On 28 Jan 2014, at 17:26, Bert Van-Den-Berg bert.van-den-b...@newcastle.ac.uk wrote: Dear all, I recently collected several datasets for a protein that needs experimental phasing. The crystals are hexagonal plates, and (automatic) data processing suggests with high confidence that the space group is P622. This is where the fun begins. For some datasets (processed in P622), the intensity distributions are normal, and the L-test (aimless, xtriage) and Z-scores (xtriage) suggest that there is no twinning (twinning fractions 0.05). However, for other datasets (same cell dimensions), the intensity distributions are not normal (eg Z-scores 10). Given that twinning is not possible in P622, this suggests to me that the real space group could be P6 with (near) perfect twinning. If I now process the normal L-test P622 datasets in P6, the twin-law based tests (britton and H-test in xtriage) give high twin fractions (0.45- 0.5), suggesting all my data is twinned. Does this make sense (ie can one have twinning with normal intensity distributions)? If it does, would the normal L-test datasets have a higher probability of being solvable? Is there any strategy for experimental phasing of (near) perfect twins? SAD would be more suitable than SIR/MIR? (I also have potential heavy atom derivatives). Thanks for any insights! Bert
[ccp4bb] twinning fun
Dear all, I recently collected several datasets for a protein that needs experimental phasing. The crystals are hexagonal plates, and (automatic) data processing suggests with high confidence that the space group is P622. This is where the fun begins. For some datasets (processed in P622), the intensity distributions are normal, and the L-test (aimless, xtriage) and Z-scores (xtriage) suggest that there is no twinning (twinning fractions 0.05). However, for other datasets (same cell dimensions), the intensity distributions are not normal (eg Z-scores 10). Given that twinning is not possible in P622, this suggests to me that the real space group could be P6 with (near) perfect twinning. If I now process the normal L-test P622 datasets in P6, the twin-law based tests (britton and H-test in xtriage) give high twin fractions (0.45- 0.5), suggesting all my data is twinned. Does this make sense (ie can one have twinning with normal intensity distributions)? If it does, would the normal L-test datasets have a higher probability of being solvable? Is there any strategy for experimental phasing of (near) perfect twins? SAD would be more suitable than SIR/MIR? (I also have potential heavy atom derivatives). Thanks for any insights! Bert
Re: [ccp4bb] twinning fun
Dear Bert Van-Den-Berg, as far as I understand this, if you have true P622, process the data in P6 and then test for twinning, both the Britton-test and H-test will indicate perfect merohedral twinning. This is because the Britton-test checks for a sudden increase of negative intensities after de-twinning, which happens only at twin fractions close to 0.5 if the intensities used for de-twinning are the same. But this is true if they are related by crystallographic symmetry. The H-test relates the absolute difference to the sum of the presumably twinned intensities, which gives 0 for intensities related by crystallographic symmetry, again resulting in twin fractions close to 0.5. In other words, intensities related by crystallographic symmetry would indicate perfect twinning in both of these tests. A better test for perfect merohedral twinning would be the ratio of I^2/I^2 which should be 2 for untwinned and 1.5 for perfectly twinned data, tested in the higher space group. These values are reported by data processing programs like XDS. Please, be aware that these ratios have rather strange values if you have an unusually high background (loop fiber diffraction, ice rings, etc.) or extremely weak data. For a really good discussion of twin tests, see Yeates, Methods. Enzymol. 276, 344-358, 1997. Best regards, Dirk. Am 28.01.14 18:26, schrieb Bert Van-Den-Berg: Dear all, I recently collected several datasets for a protein that needs experimental phasing. The crystals are hexagonal plates, and (automatic) data processing suggests with high confidence that the space group is P622. This is where the fun begins. For some datasets (processed in P622), the intensity distributions are normal, and the L-test (aimless, xtriage) and Z-scores (xtriage) suggest that there is no twinning (twinning fractions 0.05). However, for other datasets (same cell dimensions), the intensity distributions are not normal (eg Z-scores 10). Given that twinning is not possible in P622, this suggests to me that the real space group could be P6 with (near) perfect twinning. If I now process the normal L-test P622 datasets in P6, the twin-law based tests (britton and H-test in xtriage) give high twin fractions (0.45- 0.5), suggesting all my data is twinned. Does this make sense (ie can one have twinning with normal intensity distributions)? If it does, would the normal L-test datasets have a higher probability of being solvable? Is there any strategy for experimental phasing of (near) perfect twins? SAD would be more suitable than SIR/MIR? (I also have potential heavy atom derivatives). Thanks for any insights! Bert -- *** Dirk Kostrewa Gene Center Munich, A5.07 Department of Biochemistry Ludwig-Maximilians-Universität München Feodor-Lynen-Str. 25 D-81377 Munich Germany Phone: +49-89-2180-76845 Fax:+49-89-2180-76999 E-mail: kostr...@genzentrum.lmu.de WWW:www.genzentrum.lmu.de ***
