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R Hancock

Publications and source records attributed to R Hancock.

84 records · Page 5Linked to original sources
PubMed1972

Sites of replication of chromosomal DNA in a eukaryotic cell.

In mouse cells (line P815), newly synthesized DNA labeled for 20-30 sec during exponential growth is found by electron microscope autoradiography at sites throughout the cell nucleus. These sites are relatively more concentrated in the peripheral region of the nucleus (averaged over a random population of S-phase cells), probably reflecting a higher local concentration of DNA in this region. Newly synthesized DNA is not preferentially associated with purified nuclear envelopes, but is found in a fraction of the chromosomal deoxynucleoprotein whose buoyant density in CsCl after formaldehyde treatment is about 1% lower than that of the deoxynucleoprotein peak. Kinetics experiments suggest that this material is a precursor of mature deoxynucleoprotein; it may represent regions of deoxynucleoprotein containing replicating DNA and the additional proteins involved in DNA replication. Other complexes of newly replicated DNA that are found in the interphase after phenol extraction of nuclei are formed during the extraction procedure, probably due to the partially single-stranded nature of replicating DNA, and do not appear to exist in vivo.

Animals↗
PubMed1969

Biochemical evidence for induction by polyoma virus of replication of the chromosomes of mouse kidney cells.

It was shown earlier that in cultures of contact-inhibited mouse kidney cells infection with polyoma virus induces replication of the chromosomal DNA. In this paper we present evidence, based on analyses of isolated chromatin, that, parallel with and as a consequence of the virus-induced synthesis of cellular DNA, the chromosomal proteins are synthesized in the proportions characteristic of normal chromosome replication. These results are compatible with the hypothesis that polyoma virus activates (or derepresses) a regulatory system of the host cell which controls initiation of chromosome replication.

Animals↗
PubMed1965

Histones and basic polyamino acids stimulate the uptake of albumin by tumor cells in culture.

Basic proteins and polyamino acids are taken up by mammalian cells at rates up to 3000 times greater than serum albumin. When given together with serum albumin they increase the albumin uptake by a factor that correlates with their own rate of uptake and can reach more than 50-fold. The lowest threshold of activity detected (10(-10)M)is comparable to the activities of the most potent membrane-active agents.

Animals↗
PubMed1965

The initial structural lesion of penicillin action in Bacillus megaterium.

The effect of penicillin on the structure of Bacillus megaterium cells was followed in media with and without osmotic stabilization. In peptone without osmotic support the cells showed a distortion of the normal membrane-wall relationship by 20 minutes. This appeared to be a combination of both membrane distortion and cytoplasmic leakage. Lytic changes quickly followed. With osmotic support a clean-cut lesion at the transverse-septal site developed by 10 minutes' growth in penicillin. The membrane lost its normal relationship to the cell wall and formed a pocket which was filled with a fibrous material which appeared to be unorganized wall mucopeptide. The pocket of fibers enlarged until the cell either lysed or formed a protoplast.

Bacillus megaterium↗
PubMed1964

Some differences in the action of penicillin, bacitracin, and vancomycin on Bacillus megaterium.

Hancock, R. (Harvard Medical School, Boston, Mass.), and P. C. Fitz-James. Some differences in the action of penicillin, bacitracin, and vancomycin on Bacillus megaterium. J. Bacteriol. 87:1044-1050. 1964.-Penicillin and cycloserine do not inhibit the growth of protoplasts of Bacillus megaterium, indicating that inhibition of cell-wall synthesis is the only significant process by which they inhibit growth of bacteria. In contrast, bacitracin and vancomycin inhibit growth of protoplasts and bacteria at similar concentrations, indicating that they have important sites of action other than their known inhibition of cell-wall synthesis. At concentrations which inhibit mucopeptide synthesis, penicillin, bacitracin, and vancomycin each cause an increased rate of efflux of K ions from growing bacteria. This effect of penicillin is prevented by chloramphenicol or hypertonic sucrose, whereas the effects of bacitracin and vancomycin are unchanged under these conditions. It is concluded that bacitracin and vancomycin have direct effects on the cytoplasmic membrane, and it is proposed that their inhibition of cell-wall synthesis could be a consequence of these effects. Bacitracin and vancomycin do not compete with penicillin for binding to cells of B. megaterium, a further indication that they have a different primary site of action.

Bacillus megaterium↗