abstracts of papers presented at the 1962 meetings - Genetics

ABSTRACTS 967
dent maize inbred lines assayed both in 1960 and 1961. All assays were made on field-grown
plants. With only one exception, relative levels of NR activity were similar within this set of
lines in the two years, the between-years correlation being highly significant. F, hybrids showed
NR activity levels generally intermediate between those of the respective parental lines. Different
inbred lines showed widely dissimilar seasonal patterns of NR activity levels. Generally, the
inheritance of the control of NR activity level appears to be complex; no indications of “single
gene control” or “nitrate-reductase-less” mutant forms have been found. Since this enzyme has
been shown to play an important role in the nitrogen metabolic cycle of the maize plant, it ap-
pears likely that hereditary differences in NR activity could be important in the determination of
yield levels. Further studies are in progress.
LEVINTHAL, MARK, S. FOGEL, and D. D. HURST, Brooklyn College, Brooklyn, N.Y.: Genetic
and biochemical analysis of purine biosynthetic pathways in Saccharomyces.-Nine separate
genetic blocks of adenine synthesis are known in yeast. On completely specified media all mutants
produce white clones with the exception of ad-1 and ad-2. These produce a red, pink, or
buff pigment that is influenced by other loci, especially those affecting methionine, threonine or
histidine synthesis. Doubly blocked stocks containing ad-1 or ad-2 fail to accumulate pigment.
Extracts of all single mutants, ad-1 through ad-8, have been examined for the presence of
diazotizable amines via paper chromatography and the Bratton-Marshall reaction. On the basis
of the major product accumulated, the mutants fall into five classes as follows: ad-1-AIR; ad-2,
CAIR; ad-3 and ad4, AICAR; ad-5, ad-6, and ad-7, SAICAR; add, no diazotizable amine
found. The data indicate a purine biosynthesis pathway consistent with that of both pigeon
liver, Neurospora, and microbial systems. Accumulation studies concerning multiply blocked
stocks, suppressor action and effects of known genetic modifiers are in progress. (This work has
been supported by NIH Grant #RG-6979.)
LEWIS, H. W., and H. S. LEWIS, Michigan State University Oakland, Rochester, Mich.: Zdenti-
fication of a dominant second chromosome factor regulating dopa oxidase activity in Drosophila
me1anogaster.-A dominant gene (beta) has been identified on chromosome I1 which accounts
in large measure for the low dopa oxidase activity in 20-3, a line selected for low enzyme activity
from a Samarkand strain. Crosses between the 10-3 strain and a marker strain (b cn bw) yield
testcross classes whose activities in dopa oxidase units are as follows: b cn + bw/b cn + bw and
b cn + +/b cn + bw, activities >1000; + + /3 +/b cn f bw and -?- + /3 bw/b cn + bw, activi-
ties 1000. The hi-3 strain is therefore regarded as homozygous wild
type at the /3 locus. In progeny tests of individuals representing crossovers between b and cn,
b + individuals are associated with /3 activity and all + cn individuals with non+ activity.
These tests offer evidence that the /3 locus is several map units to the right of the putative struc-
tural locus, Alpha.
LIEB, M., University of Southern California Medical School, Los Angeles, Calif.: Effect of
substances that enhance UV mutation on UV induction and on photoreactivation in lysogenic
bacteria.-Methyl purines and acridine dyes will increase the frequency of mutation when
UV-irradiated bacteria are grown in their presence. No mutants are induced in unirradiated
bacteria under the same conditions. These substances have much less effect on bacterial killing.
It has been proposed that the LJV-enhancing substances prevent a “dark reactivation” process
that repairs certain UV-induced lesions, presumably in DNA.-We have studied the effect of
post-UV treatment with caffein, acriflavin or proflavin on a nonlysogenic straih of E. coli K-12
and on lambda-lysogenic derivatives. Killing of lysogenic strains was increased 5-1OX under
conditions which increased killing of nonlysogenic strains only slightly. UV-survival curves of