PubMed Health⌕ Search

Biomedical subjects

R M Benbow

Publications and source records attributed to R M Benbow.

50 records · Page 3Linked to original sources
PubMed1978

DNA synthesis in a multi-enzyme system from Xenopus laevis eggs.

Cytoplasm from unfertilized eggs of the frog Xenopus laevis was separated by DEAE-cellulose column chromatography into nine fractions. Supercoiled pXir 11 DNA molecules (pXir 11 is a Col El-based recombinant plasmid containing part of the Xenopus laevis 18S and 28S ribosomal genes and transcribed spacer region) were incubated with each fraction singly and in various combinations. After incubation for 4 hr at 26 degrees C, the pXir 11 DNA was reisolated and examined by electron microscopy. Using appropriate reaction conditions (pH 7.2, 10 mM Mg2+, 250 micron NTP, 50 50 micron dNTP, 50 MM KCl, fractions III and IV or VI), at least 5-10% of the input DNA was converted to theta structures (presumed intermediates in DNA replication).

Animals↗
PubMed1977

Recombinant DNA formation in a cell-free system from Xenopus laevis eggs.

A cell-free system is described which formed very high levels of recombinant DNA structures in 4 hr at 26 degrees C. It consisted of a single fraction of a high speed supernatant prepared from an extract of unfertilized eggs of the frog Xenopus laevis. This fraction eluted at 0.16-0.18 M Tris homogenization buffer from a DEAE-cellulose column. When two partially homologous supercoiled DNA molecules of different contour lengths were incubated simultaneously in this system, high levels of heterologous figure eight DNA structures were formed and observed by electron microscopy. Subsequently cleavage of the newly formed figure eight structures with Bam HI and Eco RI restriction endonucleases gave rise to "alpha structures" and "chi structures." The observed figure eight structures presumably represent the recombination intermediate predicted by the Holliday model for genetic recombination.

Adenosine Triphosphate↗
PubMed1975

Recombinant DNA molecules of bacteriophage phi chi174.

Phi chi174 DNA structures containing two different parental genomes were detected genetically and examined by electron microscopy. These structures consisted of two monomeric double-stranded DNA molecules linked in a figure 8 configuration. Such DNA structures were observed to be formed preferentially in host recA+ cells or recA+ cell-free systems. Since the host recA+ allele is required for most phi chi174 recombinant formation, we conclude that the observed figure 8 molecules are intermediates in, or end products of, 1 phi chi174 recombination event. We propose that recombinant figure 8 DNA molecules arise as a result of "single-strand aggression," are stabilized by double-strand "branch migration," and represent a specific example of a common intermediate in genetic recombination.

Cell-Free System↗
PubMed1975

Cytoplasmic control of nuclear DNA synthesis during early development of Xenopus laevis: a cell-free assay.

Nuclei isolated from nondividing cells were induced to synthesize DNA by incubation with cytoplasm from early embryos of Xenopus laevis. Numerous replication eyes were formed in the nuclear DNA molecules, and high levels of [3-H]dTTP were incorporated. With this assay a protein(s) which appears to initiate DNA synthesis was found at high levels in the cytoplasm of eggs, blastulae, or gastrulae, but only at low levels in the cytoplasm of oocytes, hatched embryos, or adult tissues.

Animals↗
PubMed1974

Genetic recombination in bacteriophage phi chi 174.

Genetic recombination in bacteriophage phiX174 usually takes place early in the infection process and involves two parental replicative form (double-stranded) DNA molecules. The host recA protein is required; none of the nine known phiX174 cistron products is essential. The products of a single recombination event are nonreciprocal and asymmetric. Typically, only one of the parental genotypes and one recombinant genotype are recovered from a single cell. An alternative, less efficient recombination mechanism which requires an active phiX174 cistron A protein is observed in the absence of the host recA gene product.

Alleles↗
PubMed1972

Deletion mutants of bacteriophage phiX174.

Mutants of bacteriophage varphiX174 have been isolated that are less dense than wild-type varphiX particles in CsCl. When mutant viral (+) strand DNA and wild-type complementary (-) strand DNA are hybridized, the resulting duplex molecules have single-stranded loops characteristic of wild-type-deletion heteroduplexes. The mutant bacteriophages fail to complement varphiX amber mutants in cistron E. We conclude that the mutant viruses have deleted approximately 7% of the varphiX genome in the region of cistron E.

Carbon Isotopes↗
PubMed1972

Direction of Translation and Size of Bacteriophage phiX174 Cistrons.

Translation of the bacteriophage phiX174 genome follows cistron order D-E-F-G-H-A-B-C. To establish this, the position of a nonsense mutation on the genetic map was compared with the physical size (molecular weight) of the appropriate protein fragment generated in nonpermissive cells. Distances on the phiX174 genetic map and distances on a physical map constructed from the molecular weights of phiX174 proteins and protein fragments are proportional over most of the genome with the exception of the high recombination region within cistron A.

Journal Article↗
PubMed1971

Genetic Map of Bacteriophage phiX174.

Bacteriophage phiX174 temperature-sensitive and nonsense mutations in eight cistrons were mapped by using two-, three-, and four-factor genetic crosses. The genetic map is circular with a total length of 24 x 10(-4)wt recombinants per progeny phage. The cistron order is D-E-F-G-H-A-B-C. High negative interference is seen, consistent with a small closed circular deoxyribonucleic acid molecule as a genome.

Journal Article↗