November 10, 1956

Dr. S. Spiegelman
Urbana, Tl.

Dear Sol:

Morton has checked through many of the mutants in more detail, both
with ONPGase and allelic determinag$ions. It turns out thet W-3133 is a
two-step mutant, 1.6., one step past Lacy.) = Y-~87. It gaps as a deletion
against all the other Lac, mitants; from phenotype, I would be suspicious

that it overlaps part of the Lac, cistron (a formation that looks plaud@éble,
but is somewhat beyond our presefit data]. We don't know yet whether a two-
point mutant would be distinguishable from a deletion by current procedures.

The map looks something like this now: (Don't take the sequence too seriously)

temas ene me

Se erentnandamamaebenatand

Our microscope is a Zeiss GF 595 with Neofluor objectives (except for 40x
where the achromatic seems better) and LII 2/6 condenser outfit. I an
sure Kessel can tell you exactly the setup he sold us, ani why.

Sincerely,

Joshua Lederberg