NI * . 7 — " ge Fa a ' : at = thot. 2 es i > Ss ; HE PosGidomeD CHK” LONDON. B'? Hane l Hatta BE gh Ft ae aff Pom ey Ppt a eee speash te ... £ibst before " sure whether ,affer all,your ne Ye tod abdd -dasd oftwe T .ameecmerds ic did SO Tow chevy sankey Pig UNIVERSITY | OF , ry 4 } te ee ve el ope ee eee: Pr. ~ my ae om 7 yffetsecaa on ad unlebucte er LONDOQNes 5 to tens? vas Rogt Vv bat : : PoOYRTE Ns TEE COPTER SMPTE a EP Ni ‘sig POSTGRADUATE M SCHOOL 20077 y Oop pig opt OF “LONDON od. pe fea FP 3 & a ¥ : BES gi Bu a + Pleo ah pie from. — 19%, FERS DUEANE ROAD: i el 2 wee - efoesa To prtteepnong ot $2 s5 gs be oe ot MH OTS ons 2. pak ayy Pe aan Blight BNO ges Paka SRE RMP Brea "8 LONDON, W.12" | Does teens: « Sle Ft, BROPE RMA Gy... 20thDecember, 1952... 2 ‘omtot spn tie a cccbeugyh jf sntigeie ! owe tuedes auast ‘ eft 5 , Sey matt ; ome ey 4 ny tt Ok, ri 4 cree P sk ‘ focgioy, pte, Many letter. A few maint sof -pusiness maximum number they. can send the, Author is 200 + 25 free. Institutes, however, are allowed 500... 1 have where ore doné the ‘best, I can ‘for you and: arranged for. you to have. 225 and thé Institute to get 300. : The oop Wen geteati Tp 7 tobe HUY Many. thank . for. . Ccl.S, have agreed to this sq you wiht in effect ‘have ‘not ‘far short ‘of O.you wanted... Standfast ryng up the other day and said he was not ; 7 | w ending could go in‘sincée the rather” ‘axtensive déletions,,méan that. 4 whole ‘page would probably ‘be left ‘blank. _.. T have,.thenefore. sent, him your alternative ending and he will do’ “thé best he ‘can about. it... I have sént on the (2 references and thé "stra'in No.8" alteration. I do not think the "78" would be ‘generally understood, though perhaps the general reader is not so ignorant as I! WORK: I have spent(wasted) quite a lot of time looking round for an opening in _-the K-12 story. Only within the last few weeks have I hit upon what *-geem to me to be two promising lines. The first seems closely related, | “once again,to what you are doing. Jim Watson_suggested,as the result of . the azide segregations,& probably with your FT story at the back of his - mind,that it might be worth seeing if there was any evidence of F+ segreg- “ation in the reversed 58 X W677 cross. I had only testéd 58/F+ X W/F- -.prototrophs for F+-previously. I find that whereas 100% 58/F+ X W/F- “-prototrophs are still F+,only 30% 58/F- X WF+ prototrophs dre F+! I have done 2 series on different crosses(14 & 25.prototrophs) with the same result and have a 3rd.series of 30 which will be read tomorrow. Like you,I reasaned that this is either due to segregation of to instab- ility of F+ in §8/F+,and favoured the latter since F+ is transduced to 58/F- much less efficiently than to W/F- while .a change in the cell fav- ouring instabilfty would help to explain why 58 had become F- in the first place. I ‘thought I ¢ould differentiate these two possibilities by means of F+ X F+ crosses,by. testing for F+ those prototrophs which were Lac+Mal+ and which(according to me,anyway)had been formed from W/F+ and 58 behaving as a gene acceptor(i.e.F-,either due to instability of or phenoecopy). I found,however, -that all Lac+Mal+ prototrophs from both 58/F+ &(58/F- transduced to F+)were F+ when crossed with W/F+. I had hoped to find them 100%F+ when.58/F+ was used and only 30%F+ when (F- transduced to F+) was used. This would have eliminated segregation and Linkage of F+. I hope this is clear —it is'nt very well expressed. I | suppose these results could be explicable if F+ had more than one possible locus,one being very close to Leucine(F+ being retained here in 58/F+ behaving as an F- phenocopy) and the other being just distal to B, on a y 4 i the B,-M bit of ceved fone I 411 test this but it does'nt ern very promising to me,especially since your work on FT which I take to be another facet of the same problem. . My secdhid finding is this. I normally make my crosses’ by mixing young broth cultures(either static or aerated) and washing at once.» I have done several hundred separate(but limited) analyses and the results are strikingly consistent. In analysis of 100 prototrophs from 3 separate crosses (gyre X WF-) I get 30,34 & 424 Lag+Mal- erossovers and 12,11 & 16% Az® prototrophs. when the F- parent is Az>. Analysis of 100 prototrophs from the same cross in which an aliquot of the 58/F+ culture from the ird.,cross was suspended in buf saline or 14 hrs.before mixing with W/F- gave a different result — only ing 8, Lac+Mal- c.o.s and 32% AzS,, This seems significant to me and I would explain it by supposing that the saline treatment tends to eliminate the larger chromosome segments issuing from the F+ parent and leave only those carrying TL. This will obviously require a lot of work and I also wank to try. the effect of shaking & of DNA-ase(using SM to "freeze" the ere rok Fe, ‘eulture after. washing™ ‘free. of DNA~ase) oh the’ genetic pattern of prototrophs. ... I think ft posstbte-theat- if | F+ is a. gene vector(I Have! nt ' abandoned, this idea. yet) different physical conditions may strip DNA from it in different ways and that an explanation of the F- phenocopy ‘may lie. along these lines. I willbe interested {n what you think. You will be interested | to ‘hear that I“learn T will be ‘asked "to. contribute to the next Cold Spring’ Harbor Sympdsitm ‘on viruees!" ‘It ..; S$eems.a bit thin. to me & I will Clearly have to work hard at this end of; the business. _ Iam sorry ‘you wo'nt be there,but I suppose that if _ this aspect of .the K-12 story. was considered worth oe SM & UV bx Es Bane me -preferent ial. ong it hement =» , Best of Luck _ .