.. ponderance of evidence for coli seems to be that there is a simple ;

Dec. 10, 1947.

Dear Ed- _
The genetic aspects of the carbohrdrase mutation program concerning . .
which I have written. hefore have come to a head and have to wait now  .
for the chemistry to catch up.It may be a long wait, Firstly to mall _ .

over the possible approaches, and secondly because J an not to. well
equinpved as yet (e.g. Warburgs). ae
The genetical fact is that Y-53 and W-45 which are both Lactose-_ -
nerative, the one in T-IeR,- stock, the other in B-N-, recombine to _
give a fairly large proportion (20-30%) lactose-positive prototrophs.
The obvious loopholes have been checked, and the experiments repeated,
so that in my mind there is little doubt that mutation at either one
_of two loci yields the lactose-negative phenotype. The finally tack
in the céffin, demonstrating the recovery of the double-Léece mutant
is being sought now. The locus of Lac, is as shown on the published.
map. Lao, is between BM and Lac,, ohly a few units from BM. The smoke
about phenyl galactoside utilizkt tion is due to there being two Lac —
loci, and hasn't been entirely cleared up , but seems to be controlled.
by only one of these loci:
The chemiaal problem is: how many enzymes can there be in bringing
Lactose into the ooimmon pathway of carbohydrate metabolism. The pre-

  
 

- lactase which hvdrolyses lactose. Even if the pathway were phosphoro
lygtic, there need be but a single step. But most important,how to >
prove whther there is one or more than one ensyise involved. The rub.
is that laoto-zymase is adaptive, so that any enzymatic | ‘block along ...
the way, by preventing the utilization of the carbohydrate, could pre-
vent the formation of all the other enzymes. For this reason, mixed-
juice or mixed resting cells might be inconclusive, but they haven't
teen done vet. If you have any ideas on the subject, let me know. -__
Another thing that has to be done is to straighten out the phenyl-
galactoside story, there might he a lead there.

Starting with a successful accident, I am Leaving. minerals out of
the mininal medium now. If anything they grow better than with them
in. I got no response of Y-132 to glycine + arginine. Rakkxiks
The glzeine tube fanally adapted, but this is not a growth response.

Ttll run it dovn again along with a batch of Y-120 doubles I've been
picking wp. . :

Please keep the lactose story entre-nous, or at lcast within OBL
for a while.It'ts too early to be sounding taps to the 1:1 theory.

‘Sincerely,