. Department of Genetics University of Wisconsin Madison, Wisconsin June 28, 1949 AI9 MAIL -- Dear Cavallf : Ym informative letter just received. Enclosed find an aypm?.i~ with a summary of my data on the cross of S&i61 with W-585. I 8m pleased that we should have made so nearly the, came obsel-va- tione on the linkage relationships of Ma1 and Gal. I don't ze(a how Ma1 eaz~ be put on ths ma? at all! Once I thought that it d&t be between B and 14 (which would ma& any linkage either to Lac or to Bl, but this has been e%otded by crosses in which both biotin and thiaine were added to the medium. N- is exceedingly stable, ao that it is possible to use it alone. If Mai were be- tween M and 31, it should car&uainly interact much more etrongly than it does with 31. It cannot be t-o theleft of Bl as it shows a closer linkage, wi+A BM, and does not interact strongly with %. ff Ma1 ia in linear order,. on8 would . have to Flace it not far from 31, aad aaeme a non-random distribution of crossing over. I would rather relate Nal ptjculiarities to the fact that it is almost illvariably hemizygons izx ths heteronygotes. If the zygotes from klliich prototroshs are isolated are comparable (except for persistence) to the hetero- zygotez, then on8 wdd get an qparent linkage based on the fact that in some way Mati is almost always lost! The 8ame probably appi&e to Gal. I've just completed some reversion experiments on Gal- heteroaygotes which show that Gal is also hemizygous. Howeme, whereas the heterozygotes (from a cross involving W-583) are almost invariably Mal- (hemizygous Mal-), many of them are either Gal- or Gai#. The Gal factor of W-583 has never been obaerved heterozygons, end only recently I have found the first instance of a Ma1 heterozygote. Heterozygositg . 4y _.., _._ -I' PZLge2- June 28, 1949 for Ma1 is certainly very rare indeed, e.nd possibly may arise from quite a dif- ferent meahanism than the other aneuploid heterozygotee. I really still do not have a good story on the mechanisms of this heterozygote, but thfa summ8r for- tUXb8iy, I have a good deal Of assistanae, and am approaahing the problem on a zuitably large scale. We need mostly some good information on the inheritance of a, but ao far only the A, B, and (1 stocks mentioned in ~qg paper haye carried it. In your letter you refer to the possibility of oonfusion based on the epistasis . . of Gal,+ to Lac-. I wonder if you do not kve a typographical.error. If Gal$ were epistatic, then the standard Lac- stocks (e.g. Y-53 or T-87) could not be recoe nized as such, since they are Gal&. Gal- ia aepistatfcff to La#, in the sense that it is sometimes difficult to soore a Gsl-Laci) as Lae#, i.e., the Gal- weakans the iaetose fermentation. I must certainly agrse with you about the difficulty of scoring Are. I hW8 not used it to any extant. IC, seems to be almost completely linked to Gal. I was interested ia'your observation abxt tixed prototroph eolo.nies. I have seen them ra Lao, espeoially by conducti% the crosses on synthetic EM3 lactose, where they cm be seeu diractly as colonies with integral sectors. However, Ihad the i~rassion that rather less than 15 of the colonies were mixad for tic. On kltose EMS, more than 105 of the (few) IJal# prototrophs also have a Xk- sector. I have thought of these as likely to be sister neiotic products, because thera ara distinct correlations in their Lac aad ? segrsgations which one would not eqect from dlstinut zygotes. On the other hand, f think there is a good prima facie case that the mixed prototrophs you get from year Hfr crosses are likely to some iron several zygotes. \I You point out yourself the extent of microcolony formation. If the rate of recoz- . . - bination is high, one would have to &ect that several cells from a microcolony at a &Yen p&u?8 till each paSticipat8 in a fusion and produce Several zygOt8s. , a9e3- June 28.1949 . siZkCe YOU &VS SOm8 hint Or an f-1 test Of wr, I assume thrrt you hzve succeeded I in recovering mnlfiple mutant as well as prototrqh reaombinants with its help. As you may imagine, I am~exceedingly interested in t:lis atock, and would like verymuch to have the -portunity of confirming your observations. you aan be sure that ycm will be kgt fully informed of any ffndings, and that we will. make no attempt to intrude on any area in which you would be particularly interested. If you agree to send it, I: would be most appreciative. However, r hope that this request vill not em'oarrass you, as 1 can wei understti t-hat you might have some reticence abmt distributing it so early in your investigation. I gather that you are . . active4 pursuing the problem of the'mochanism whereby Hfr is-more active thsn 58-161 in producing prototrophs. Have you considered the likelihood i&t it msy b8 mu& mars motile? X have often thought that their tight be a chenotro$sn between distinct mutants, for each pro&aces the needs of the other, and some such Fhenomenon might dfs~30s8 of ths kinetic difficulties. Lately, I have realized that some of my stocks ax9 consistently Lfr (low frequency of recombin.&ion) for no obvious biochemical reason. This has been particularly true of crosses of Lacp with Lz-, even on glucose medPxn on which either of them grow very well with proper supplements. I have iso noticed this among a number of segrsgants from H- stocks, agailrlth no obvious chenid basis. f have hoped to use these &fr stocks t? 8XplOr8 enViroment83 COnditiOn_ -&i.zh might sti;rmlate recombination, thinIcing that the "standards rate was naarly all . one 0ouI.d expect onkinetic grounds. I will be glad to sand you some of these if they would help your analysfs. . Secondly, one of the most prqmisl~lp, leads ia the investigation of the hetem- zygotes has been the finding &at some segregants give markew altered ratios cf Iad and Ma19 protokrophs (both graatljr inoreaS8d) compsred to biochemically ocst- parable stocks. !Chis tends to support the notion that a chromosonal. aberration is involved, but is still faz from definitive. . --- ----___ wize4- June 28.1949 With all of the confusion uonaerning the linkages of Gal and Mal, I wonder whether you may not be very acetical abont linearity. Certainly 1 would bel However, mag I suggest that you sometime tq the V6-Lac-Vl series mentioned /- in npr Genetics paper which gave quite cleancut results. Yours very sincerely, Joshua Lederberg /w P.S. on looking over my notes, -X flnd,that X cannot give you any worthwhile account of the crosses.1 did with 58-161 x W583. 1 noticed that there were very few Gal# Law or Gal- La&, but decided that I couMu*t score the latter at all. Later I noticed that 35 lactose facili+Wxd scar%=, but X hamutt ussd this to collect quautitative data. Bowever, hers am some scores for maltose.aud galactose. , ; X-G# !4$G- wc# 34 10 s 2 4 (0) ExD. 353 43 15 2 0 '1 (21) when I realized that G-L# wa's diffi< to score, I abandoned W533 and used ~677 which has the other disadvanta&e that Gal itself is difficult to read. f sm tr&g to per?ect better stocks. These data certainly put Gal and Mal rather far wart, and I still wonder whether && lsa*t mar Lac, as you bdicate. Your data show ab%xt $ triples. This & disturbingly high (like table 6 in my Genetics paper) but it seems to be so!