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December 14, 1952

Dear Norton:

I am delighted to hear of your substantial progress on the mouse—virulenee
problem. Are you sure that nothing can be found in vitro that would parallel
the animal experiments?

Ssybalski made up that quotation-— I never said it, though I might well have
meant it.

Sorry to have to press you so, but what I wanted as a "definition" of a lytic
variant was just which phage and indicator systems you had in hand. I may have
overlooked this in an earlier letter from you.

You may be interested in some more on lysogenisation/transdug: n. This time
the compariaon concerns the incidence of lysogenicity in Gal*PMa (added) and
in Gal Fia™ (transductions »from Gal“¥ia~) selected on EUB Gal. The results: :
the added Gal” were 3 Lp*:43 Lp®; the transinduced Gal+ wee 18 Lp+ : 3.1988"
The only trouble is that we do not know what limits the inoddence of lysogeni-
city in this system. I have some other experiments in the works where the’

limiting factor 1a the amount of phage. The correlation seems already secure.

     

Your cryptic note some time ago Kphage = Kp, = 90 should, I take it, be
interpreted as 80/ginute, and not 80/second or 80/hour, in the expression

v=¥, eitte, Dave finally pulled out an FA serum he had started ages ago. It
titrated, roughly,to about 50/min. I haven't so far checked your comparison
of FA and phage.

I was inferested to see whether one could not break up the action of the
presumed H," Fla, complex in the linked transduction by means of DV. I was

rather surprised to find that the Inactivation of transduction was almost negli-
gible (following the initial activation) even with tremendous doses. With such »
exposures as 20 minutes (sic!) at 50 cm., phage titres of about 100 - 1000 /ml
are associated with approximately equal or higher transductive activity. I've
looked most at Gal+ from SW-666, using phage 22B, but Fla’ behaves similarly,
and one experiment with PLT22/2 on SW435 /D(o) gave essentially similar results
(this 15 still inoubating). One can easily count plajues and Gal+ on the same
plate. I haven't tested the lysogenicity of the latter so far. Thisseems to be
discrepant with your previous findings, but I can't find any record of them here.
This might be useful in practice with other gystems—e.g. your virulent mutant,

With Larry's help, I'm also looking into FA in lwoffates. SW~666(PLT22B) seems
to be working moderately well; most other systems not. The phage so far has general
transducing activity, but I'1]1 send you the details when theg're worked out.

Bincerely, _
*undoubtedly overestimated owing to Joshua Lederberg

the possibility of mitiplicity reactivation.
The joapetentien curve definitely flattens out as expected on this basis.