June 11, 1946+

Dear Sol:

Thanks for your very prompt respponse- something I amacaustomed neither
to receive nor dispense.

I'm sorry I did not mke myself clearer. For the production of detectable
mutants, haploid populations are essential( although the presence of a small
proportion of diploids would not be too disturbing)+ A haploid single ascospore
culture of S. cerevisiae would be ok for this(provided it did not undergo
'‘4llegitdémate diploidization') Once having gotten mutants, I thought genetie
analysis might be possible by plating out asci (derived from the fertilization
of the haploid vegetative cells at random, ie a 'sporulating culture') and
then analysing the components of the colonies derived from the asci, by
replating/ them individually. If cerevisise can be kept haploid there is
no reason why it could not be used, except that in the Saccharomyces spp.

@ manual mpm separation would be required to obtain haploid cultures
from the asci. I would not mind trying to use the micromanipulator
but I never have done so. Since you think it feasible, I would appreciate
a copy of any good cerevisiae strain, but in particular haploid isolates
of different mating types. Any information (or refermmces) to the
biochemical geharacteristice~- in particular the vitamin requirenents- of
such strains would be particularly abportant. To go back to pombe-
do you have any evidence of mating type differentiation in this strain?
I thought 'haploid', ‘single ascospore' cultures would diploidize and
sporulate fairly readily under certain conditions.

Work on the bacteria hasn't gotten too far- a variety of mutants have
been obtained in several different strains of E. cold with uy? and I'm
working on the tine of appearance after radiation. “dncerely, Johhua.