Deer Francis,
pre-

You may remember mentioning agi medical stud-:nt naned Zinder or sonsthing
Like that as a possible good candidate for a yserts work here under ar.
assittantship. Ie he interested? I gawen't heard from him.

The mitants get to be more commlicauted all the tims. A temperature
sensitive allel of lac; has been found which is 1.ao-Glu-Sorbitol- at 40°

(as Lac,— ig at all temperatures) but is Aff at 30. At 32 itis 4,

3
at 36 it is 4. ! This sertainly seema to be a pleiotropic mtation in
every sense of the term. I don't see how it is going to be possible te
ascertain the primary effect of the gene, but something may turn up.

Vital dyes for coli might interest you in facilitating observation
of mierocolonies. The redox indieatar 2,3,5 triphenyltetrazolium chloride
may be a good bet. In the presence of an oxnidisable substrate, coli cells
reduce this colorlese sempound to the red, insoluble formazan derivative,
and for reasons yet unknown accumulate the pigment in (usualig) a single
granule near one end of the cell. The mleroseopic picture is very striking]
You oan get the compound as "HZ reagent from Paul Lewis Laboratories,
4253 W. Pt. Washington Road, Nilweukee 12, They probably will be glad to give
you a gram ar so gratis, Bven merely ae an ensyme iadicator, this compound
probably has wery good potentialities.

Best regards,

Joshua Lederberg