Biomedical subjects

M Russel

Publications and source records attributed to M Russel.

6 recordsLinked to original sources

PubMed1992

Construction of a microphage variant of filamentous bacteriophage.

The intergenic region in the genome of the Ff class of filamentous phage (comprising strains fl, fd and M13) genome constitutes 8% of the viral genome, and has essential functions in DNA replication and phage morphogenesis. The functional domains of this region may be inserted into separate sites of a plasmid to function independently. Here, we demonstrate the construction of a plasmid containing, sequentially, the origin of (+)-strand synthesis, the packaging signal and a terminator of (+)-strand synthesis. When host cells harboring this plasmid (pLS7) are infected with helper phage they produce a microphage particle containing all the structural elements of the mature, native phage. The microphage is 65 A in diameter and about 500 A long. It contains a 221-base single-stranded circle of DNA coated by about 95 copies of the major coat protein (gene 8 protein).

Bacteriophage M13↗

PubMed1992

Interchangeability of related proteins and autonomy of function. The morphogenetic proteins of filamentous phage f1 and IKe cannot replace one another.

The filamentous phage f1 and IKe infect a common host, are structurally highly similar and exhibit 55% identity at the DNA sequence level. Based on the idea that proteins that function autonomously will be more tolerant of multiple amino acid differences than proteins that must interact with other proteins to function, the ability of four individual proteins from f1 to substitute for their IKe equivalents to promote virus assembly in vivo has been examined. The reciprocal replacements were also examined. Only the single-strand DNA binding proteins (pV) were fully interchangeable. A minor capsid protein, pIX, was unable to substitute in assembly of the heterologous phage. Two proteins required for particle assembly that are not part of the phage particle, pI and pIV, were not interchangeable, although pIVf1 stimulated formation of a very small number of IKe particles in the absence of pIVIKe. The lack of interchangeability suggests that these morphogenetic proteins do not function autonomously, but rather interact with one or more phage proteins. The ability of certain overproduced proteins to interfere with assembly of wild-type f1 or IKe forms the basis for a model that suggests that phage assembly requires an interaction between pI and pIV.

Cloning, Molecular↗

PubMed1992

A modified TnphoA useful for single-stranded DNA sequencing.

The TnphoA transposon constructed by Manoil and Beckwith [Proc. Natl. Acad. Sci. USA 82 (1985) 8129-8133] has been modified to permit easy isolation of single-stranded (ss) DNA of target plasmids. The intergenic region (IG) of filamentous phage f1, which consists of the phage origin of replication and packaging signal, was inserted into a nonessential region of TnphoA. This modified transposon should be useful for the analysis of genes cloned in plasmids that lack a filamentous phage IG. Transposition of TnphoA-IG into a plasmid carries the IG with it; subsequently, after infection with a filamentous helper phage, ss plasmid DNA suitable for sequence analysis and useful for oligodeoxyribonucleotide-mediated mutagenesis of TnphoA-generated fusions can be isolated. The utility of TnphoA-IG was confirmed by analysis of 'blue hops' into the bla (encoding beta-lactamase) and pspE (encoding phage shock protein) genes whose products are secreted into the Escherichia coli periplasm.

Alkaline Phosphatase↗

PubMed1991

Filamentous phage assembly.

Filamentous phages present a genetically well-defined system for studying the ordered membrane assembly of five different phage-encoded proteins around the circular single-stranded DNA phage genome. Assembly occurs at high efficiency in vivo, catalysed by two phage-encoded membrane proteins and at least one host protein, thioredoxin. This review presents a description of the virion and its cytoplasmic precursor and summarizes the results of genetic and biochemical experiments that are beginning to elucidate the role of the three morphogenetic proteins. The recent discovery of bacterial transport proteins with homology to a phage morphogenetic protein located in the outer membrane suggests the existence of a common mechanism for moving complex macromolecules across bacterial membranes.

Amino Acid Sequence↗

PubMed1976

Regulation of gene 32 expression during bacteriophage T4 infection of Escherichia coli.

The gene 32 protein of the bacteriophage T4 plays an important role in genetic recombination, DNA repair, and DNA replication; the protein functions in these processes by virtue of a strong binding capacity for single-stranded DNA. During infections of Escherichia coli by bacteriophage carrying amber of temperature-sensitive mutations in gene 32, the altered gene 32 protein (that is, the amber fragment of the missense polypeptide) is synthesized at greatly elevated rates. During infections by phages that are mutant in other genes (and wild type in gene 32), gene 32 expression is coupled to the quantity of single-stranded DNA produced during the infection. The data are consistent with a model in which the gene 32 protein binds preferentially to all available single-stranded DNA. When all available single-stranded DNA is complexed with gene 32 protein, free gene 32 protein represses its own synthesis. The high level expression of altered gene 32 proteins (amber fragments or missense polypeptides) is a direct consequence of the proposed autoregulation.

Coliphages↗

PubMed1976

Translational, autogenous regulation of gene 32 expression during bacteriophage T4 infection.

Functional half-life measurements of the bacteriophage T4 gene 32 messenger RNA indicate that this mRNA is extremely stable. Regulation of gene 32 expression at the transcriptional level cannot account for the rapidity with which P32 synthesis can be repressed. Furthermore, derepression of P32 synthesis occurs in the presence of rifampicin, a drug which inhibits transcriptional initiation. In addition, T4-infected cultures in which P32 expression is repressed possess almost as much gene 32 mRNA as derepressed cultures. We conclude that expression of the T4 gene 32 protein is regulated at the level of translation.

Coliphages↗