abstracts of papers presented at the 1962 meetings - Genetics

996 ABSTRACTS
observed in p-galactosidase production. This characteristic lag was not observed in a constitutive
mutant of E. coli 58-161. Therefore, it seems that, in E. coli 58-161, a repressor of ,&galactosidase
accumulated concommitantly with RNA during methionine starvation. This repression is how-
ever, not reversible by an inducer of P-galactosidase.
YOON, C. H., and S. LIZIO, Boston College, Chestnut Hill, Mass.: Evidence of incorporation of
tagged DNA extracted from thymus glands into germ cells of recipient mice.-DNA of the
thymus glands of mice was tagged with P32 and was extracted. This extracted DNA was then
injected into gonads of recipient mice. Evidence that indicates that this tagged DNA was incor-
porated into DNA of germ cells of recipient mice was obtained.
YOSHIKAWA, HIROSHI, and NOEKIRU SUEOKA, University of Illinois, Urbana, Ill.: Mechanism
of chromosome replication in Bacillus subti1is.-A series of experiments were designed to test
two major alternative models of chromosome replication by using genetic transformation system
of B. subtilis. Model A (random-in-time replication) : replication of DNA in the chromosome
occurs simultaneously in the whole region of the chromosome without any oriented sequence
along the chromosome. Model B (oriented replication) : replication of DNA starts from one or
both ends of the chromosome and proceeds orderly. The principle of our experiment is to culture
a wild type strain in a heavy meclium containing deuterium and nitrogen-15, and transfer to a
light medium (H20, NI4). Cell samples are taken at 0, %, K and 1 generations after the transfer.
DNA from each sample is centrifuged in CsCl solution, and heavy and hybrid DNA molecules
are separated by collecting single drops from the bottom of the centrifuge tube. Measuring the
specific transforming activity (STA) of 12 different auxotrophic markers in heavy and hybrid
DNA molecules, it is predicted that if the random-in-time replication model is right, the STA's
of both heavy and hybrid DNA should he similar, while in the oriented replication model there
should be difference in STA's between heavy and hybrid DNA. Moreover, in the latter model,
each marker should give a distinct ratio of STA's in the two DNA, depending on the location of
the marker in the chromosome. The experimental results so far obtained are consistent with the
oriented replication model. Results of further experiments on this line will be presented. (This
work is supported by National Science Foundation grants G-15080 and G-18745.)
ZALOKAR, M., University of California, La Jolla, Calif.: The role of nucleolus in the production
of ribonucleic acid.-The incorporation of H3-uridine into RNA of oocyte nuclei of Blatella
germanica was studied by autoradiography. When oocytes were incubated in H3-uridine for
four to 16 minutes, the newly formed, labeled RNA appeared in both nucleoli and chromosomes.
Nucleolar RNA was first observed in several spots at the periphery of the nucleolus. After one
hour or longer incubation the nucleolus became uniformly labeled. These observations indicate
that nucleolar RNA was produced at the periphery of the nucleolus, where the presence of DNA
could be demonstrated. It is probably not the nucleolus itself which pnoduces nucleolar RNA,
hut this DNA belonging to the chromosomal regions adjacent to the nucleolus. Experiments
with Actinomycin D showed that this DNA is functionally different from DNA in the rest of
chromosomes. When oocytes were incubated in H3-uridine in the presence of 2 pg/ml of Actinomycin
D, nucleoli remained unlabeled, while chromosomes became labeled nearly as strongly
as in the absence of the drug. At higher concentrations (IO pg/ml) Actinomycin D inhibited
both nucleolar and chromosomal RNA production. In conclusion it appears that the nucleoli serve
as intermediate storage or processing place for a certain kind of RNA, produced by particular
regions of chromosomes. The problem of transfer of chromosomal and nucleolar RNA into the
cytoplasm is now being studied by inhibiting new RNA formation with Actinomycin D.
ZAMENHOF, S., and ROSALIE DE GIOVANNI-DONNELLY, Columbia University, New York, N.Y.:
Heat-induced "coupled" mutations in B. subtilis-Among nine histidine- mutants obtained by
heating spores of the originally indole- strain 168 of B. subtilis, three have lost or altered this