evil

December 5, 1955

Dear Aaron-—

I hac some second thoughts about lactase which I sibourkxoos had not
clarified during our discussion.

If you accept the existence of a "y-system" in Lac+ strains, it seems
to me you are going to have compkications in evaluating any of your other
experiments without measurement and control of the intracellular inducer
concentration. Now I think we are agreed that there is some system for
accumulating TMG which is more active in induced than in noninduced cells.
But why not then use Lac, , which according to Monod differs in the lack
of any concentrating ability (presumably even in cells induces with TMG
and othar substrates)? I believe it is correct that TMQ (as well as MG and
BuG) will induce Lac,. If you can still find the maintenance of “duplicons"
at threshold levels of TMQ, you have prima facie evidence against the neces—
sary role of the y system in the perpetuation of the high ard low states
of the cells, a point which would be subject to direct test with isotopically
labelled inducers. The main trouble my be that higher ooneentrathons of in-
ducers my be necessary, but this is not so serious a trouble, since you
would avert the other problem of a unique intracellular level. If this works
out, you can also use tim lactose as a non-inducing subssrate (14 the presence
of threshold TMG) as a colony—indicating score for the two states.

I think you have as suitable Lac.” stocks as I could give you.

By the way, 1 forgot what you told me about the r-equivalent of a cup
of coffees. Could you also give ms r-yield of atations (have you published
this?) and the references to the pharmacodynamles of caffédie? (as well
as the pH-gradient-elewtrophoresis technique?

It was a swell visit; we ottght to mix more often.