Biomedical subjects

R M Walmsley

Publications and source records attributed to R M Walmsley.

20 records · Page 2Linked to original sources

PubMed1983

Is there left-handed DNA at the ends of yeast chromosomes?

Tracts of the alternating copolymer poly(dGdT . dCdA) have been observed in a variety of eukaryotes. Such tracts are of particular interest since homopolymers of this sequence can exist in vitro as left-handed Z form DNA. We have found that the yeast Saccharomyces cerevisiae contains at least 30 poly(GT) tracts at dispersed genomic locations. We show here that one subset of these tracts is located at the ends (telomeres) of the yeast chromosome. In addition, we show that poly(dGdT . dCdA) tracts are added to the ends of the extrachromosomal ribosomal DNA molecules of Tetrahymena when cloned in yeast. These data represent the first reported association between a homopolymeric sequence and a chromosome structure.

Base Sequence↗

PubMed1983

Stability of a cloned gene in yeast grown in chemostat culture.

A study has been made of the stability of LEU2, a cloned chromosomal gene of Saccharomyces cerevisiae, when reintroduced into yeast on a number of plasmid vectors which permit a chromosomal or episomal location for the gene in either high or low copy number. Glucose-limited continuous culture was employed to ensure that there was no selection for the inserted gene. Both the rate of segregation of plasmid minus cells and the effect of the plasmid on host growth rate were found to determine plasmid stability which, in many cases, could be predicted by simple mathematical models. The presence or absence of the endogenous 2 mu plasmid of yeast was found to have an important influence on the stability of 2 mu-based vectors. This led to the discovery that, for the host strain used, the presence of 2 mu sequences represented a selective advantage for the cells.

Cloning, Molecular↗