abstracts of papers presented at the 1962 meetings - Genetics

ABSTRACTS 989
sulfate concentration than the activity of the wild type. Further, the heterocaryon enzyme is
significantly more heat labile than wild-type enzyme, and Km’s for pyridoxal-phosphate and
indole in the reaction are tenfold higher in the complementation than in wild-type enzyme.-
The independent extracts of the above two mutants possess CRM, a protein serologically related
to tryptophan synthetase. The CRM’s however, differ in their ammonium sulfate fractionation
patterns and heat sensitivities. The two different ammonium sulfate fractions made from the
heterocaryon extracts contain different amounts of each CRM. No significant differences were
found between the two fractions in Km’s for serine, pyridoxal-phosphate and indole, and their
heat sensitivities. From these studies, it is concluded that the complementation enzyme is differ-
ent from wild type and perhaps a single species of the active complementation enzyme is
produced.
SUYAMA, Y., and D. M. BONNER, University of California, San Diego, La Jolla, California:
Complementation, mutation and enzyme alteration in the tryptophan synthetase system of
Neurospora.-Mutations at the locus which controls the formation of tryptophan synthetase
produce diverse alterations of the enzyme. It is known that extracts from some mutants possess
CRM (a protein serologically related to tryptophan synthetase), while others do not; these are
designated as CRM’ and CRM- mutants, respectively. Differences are also found among CRM’s
in terms of their ability to catalyze the three reactions which are catalyzed by wild-type tryptophan
synthetase.-It is of interest to relate the complementation properties of these various
mutants to the nature of their enzyme alterations and to the location of the mutational sites
within the locus.-The present studies demonstrated that complementation is not found between
mutants possessing catalytically similar CRM or between CRM- mutants and that three complementing
units can be assigned in terms of genetic segments and catalytically competent segments
of the enzyme. Further, the observation that the complementation map is not linear,
suggests that complementation is not a direct reflection of the primary structure of the protein
but rather a measure of complex interactions between functionally competent segments of the
polypeptide.
SUZUKI, D. T., Biology Division, Oak Ridge National Laboratory, Oak Ridge, Tenn.: A pos-
sible role of asynapsis in interchromosomal effects on crossing-over in Drosophila me1anogaster.-
Chromosomes having interchromosomal effects on crossing-over can be divided into two classes
based on their pairing configurations. The classic category is characterized by the formation of
synaptic loops or rings: inversion heterozygotes and homozygotes; ring X heterozygotes and
homozygotes; tandem metacentric and acrocentric compond Xs. The chromosomes in the second
class do not synapse as loops and have a reduced frequency of crossing-over: reversed acrocentric
(RA) compound X with no free Y; reversed metacentric with a Y; two rod X’s with a Y, a free
or attached proximal duplication (BS), or a free distal duplication (@). It is suggested that the
arms of these chromosomes fail to pair with a definite frequency owing to intrinsic chromosome
properties (RA/O) or competition with an extra homologous element.-Crossing-over in chromo-
some 3 was measured in females heterozygous for either FM-6, an X chromosome rearrange-
ment containing eight breakpoints, or SM-5, a second chromosome with 13 breakpoints. It is
assumed that these complex rearrangements fail to pair with their normal homologs because
of mechanical difficulties. Both rearrangements increase crossing-over in chromosome 3, the
magnitude of increase in the regions adjacent to the centromere being as great as in the centro-
mere region.-It is suggested that asynapsis of one chromosome pair is a sufficient condition
for causing an increased frequency of crossing-over in another pair. A critical test of this hy-
pothesis, measuring autosomal crossing-over in exchange (synapsed) and nonexchange (asyn-
apsed) reversed acrocentric progeny, will be reported.
SUZUKI, NORIO,
and I. L. KOSIN, Washington State University, Pullman, Wash.: The age of
RBC donors and the immunological differences in genetically isolated lines of domestic turkeys.-