Januexry 21, 1948. Dear Jacques, My last letter, on I think the 4 Nov., described a few sugar mitants that heave been picked up here. I can't remember for sure whether I sent you any of them or not. Drop me a line anc T'i] send you any of the cultures I have and mention. I am still anxious to receive your reprints, especiaily your book. I have started to do some adaptation experiments, and find that azide is a potent inhibitor of edaptation to lactose, maltose, etc. I am not clear from your papers however tader what conditions adaptation may take place. In my experimace, resting cell suspensions in aqueous lactose or maltose (plus phosphate buiier) will aaapt over @ period of several hours, in the absence oi exogenous nitrogen. To you have any comparable experiences? One of the most striking and inexplicable findg&gngs in this work has been the cross- reaction between trehalose and maltose, Trehalose-adapted cells are concémitantly maltose-adapted, but cells grown in malgtose are not tre: alose-adapted. This might suggest malto-zymase -4 trehalo-zymase, but none of the several maltose- mutants are tre- hale@ge negative. Tne work ie hindered by the high cost of tre- halese which has made large scale attempts to find trehalose- mutants unfeasible. , By selection in synthetic medium, only two "positive" mutants have been found: for salicin, and for amylose (a tuxkxknuixknz "saccharifying" amylase). Probably the most interesting finding so far is that all the lactose-negasive mutants are not by any means allelic. At least two loci have been definitely located, and there are probably others among & group not es yet ansclysed. The same holds for maltose; in addition there is a locus mutation at which leads not to maltose- but to a "slow" fermenter. I had in hand a third definitely located mutant which I thought to be lactose-, but it turns out to produce no acid even from glucose or galactoset ‘hwgher this mutant repre- sents 4 block in the glycolytic mechanism, or is the sought-after general curbohydrase-precursor ¢ene remains to be seen. I leave you to draw your own conclusions re 1:1 theory which can be inferz cd from the genetic data on lactose and maltose! Have you any sug: estion regarding a two- or n-step mechanism for the dissimilation of lactose 7. Bemethyl galactoside shows nearly the same reaction as lactose in these mutants, but butyl-b-