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Biomedical subjects

P Model

Publications and source records attributed to P Model.

At least 91 records · Page 5Linked to original sources
PubMed1981

Filamentous phage assembly: membrane insertion of the major coat protein.

The assembly of filamentous bacteriophages has been studied in cells infected by wild-type and mutant phage; host mutants defective in bacteriophage assembly have also been isolated. Phage assembly takes place at the membrane, and requires insertion of the viral major coat protein. We present data on the physiology of this process and on the effects of amino acid sequence variations near to the coat protein amino terminus on membrane insertion, processing, and phage assembly.

Coliphages↗
PubMed1979

Characterization of Op3, a lysis-defective mutant of bacteriophage f2.

We have isolated a conditional lethal mutant of bacteriophage 12 which makes plaques only on E. coli strains carrying a UGA suppressor. It grows normally in nonsuppressing hosts but does not lyse such strains. The mutation complements with amber mutations in each of the three known phage cistrons. These observations lead us to postulate the existence of a fourth gene in the RNA phage.

Amino Acids↗
PubMed1979

Binding of mammalian ribosomes to MS2 phage RNA reveals an overlapping gene encoding a lysis function.

The main binding site for mammalian ribosomes on the single-stranded RNA of bacteriophage MS2 is located nine tenths of the way through the coat protein gene. Translation initiated at an AUG triplet in the +1 frame yields a 75 amino acid polypeptide which terminates within the synthetase gene at a UAA codon, also in the +1 frame. Partial amino acid sequence analysis of the product synthesized in relatively large amounts by mammalian ribosomes confirms this assignment of the overlapping cistron. The same protein is made in an E. coli cell-free system, but only in very small amounts. Analysis of the translation products directed by RNA from op3, a UGA nonsense mutant of phage f2, identifies the overlapping cistron as a lysis gene. In this paper we show that the op3 mutation is a C yield U transition occurring in the second codon of the synthetase cistron, which explains the lowered production of phage replicase (as well as lack of lysis) upon op3 infection of nonpermissive cells. We discuss the properties of the overlapping gene in relation to its lysis function, recognition of the lysis initiator region by E. coli versus eucaryotic ribosomes and op3 as a ribosome binding site mutant for the f2 synthetase cistron.

Amino Acid Sequence↗
PubMed1979

Membrane biogenesis: cotranslational integration of the bacteriophage f1 coat protein into an Escherichia coli membrane fraction.

The coat protein (CP) of bacteriophage f1 is integrated into an Escherichia coli plasma membrane fraction consisting of inverted vesicles when it is synthesized in a cell-free, coupled transcription--translation system supplemented with the inverted vesicles. By using proteolytic enzymes as probes, we found by subsequent peptide mapping and determination of the sequence of the proteolytic products that CP was inserted into the inverted vesicles in an orientation indistinguishable from that in inverted vesicles prepared from infected E. coli: only a COOH-terminal portion of approximately 10 residues was accessible to proteolysis, whereas the remainder of CP (CP') was entirely protected. Protection of CP' was dependent on the integrity of the vesicle membrane, because it was abolished when proteolysis was done in the presence of nonionic detergents. Insertion was observed when the inverted vesicles were present during translation in the cell-free system, not when they were added after translation. Thus, the asymmetric insertion of this type of integral membrane protein is strictly coupled to translation. These findings are discussed with respect to prokaryotic membrane biogenesis and are related to bacteriophage f1 assembly and infection.

Bacterial Proteins↗
PubMed1979

Organization of a hybrid between phage f1 and plasmid pSC101.

We have characterized the 200-nucleotide-long insertion found in f1 after segregation of a chimeric phage containing the genomes of f1 and pSC101 [Ohsumi, M., Vovis, G.F. & Zinder, N.D. (1978) Virology 89, 438--449]. The insertion in this novel f1 species, called f1', is derived from pSC101 and has the potential to form an extended base-paired secondary structure, as determined by nucleotide sequence analysis. A five-nucleotide direct repeat, derived from f1 sequences, is present in f1'. The 200 additional nucleotides that are inserted into the DNA sequence coding for the carboxy terminus of f1 gene IV protein have generated a novel carboxy terminus for the f1' gene IV protein. In vitro transcription--translation studies demonstrate that a read-through protein can be expressed, as predicted from the f1' nucleotide sequence results. This 200-nucleotide-long sequence appears to be a transposable element found within pSC101 and is similar in sequence to the inverted repeat found in Tn3. Restriction enzyme analysis of the chimeric phage DNA, coupled with the nucleotide sequencing results, allows us to predict a structure for the genomic organization of this chimera.

Base Sequence↗
PubMed1979

Mechanism of export of colicin E1 and colicin E3.

The mechanism of export of colicins E1 and E3 was examined. Neither colicin E1, colicin E3, Nor colicin E3 immunity protein appears to be synthesized as a precursor protein with an amino-terminal extension. Instead, the colicins, as well as the colicin E3 immunity protein, appear to leave the cells where they are made, long after their synthesis, by a nonspecific mechanism which results in increased permeability of the producing cells. Induction of ColE3-containing cells with mitomycin C leads to actual lysis of those cells, as some time after synthesis of the colicin E3 and its immunity protein has been completed. Induction of ColE1-containing cells results in increased permeability of the cells, but not in actual lysis, and most of the colicin E1 produced never leaves the producing cells. Intracellular proteins such as elongation factor G can be found outside of colicinogenic cells after mitomycin C induction, along with the colicin. Until substantial increases in permeability occur, most of the colicin remains cell associated, in the soluble cytosol, rather than in a membrane-associated form.

Bacterial Proteins↗
PubMed1978

Detection of prokaryotic signal peptidase in an Escherichia coli membrane fraction: endoproteolytic cleavage of nascent f1 pre-coat protein.

An inverted membrane vesicle fraction isolated from uninfected Escherichia coli and largely derived from the inner membrane has been shown to contain an endoproteolytic activity that cleaves nascent bacteriophage f1 pre-coat protein into two identifiable products. The electrophoretic mobility on sodium dodecyl sulfate/urea/polyacrylamide gels and the partial amino-terminal sequence of the larger fragment were indistinguishable from those of the mature phage coat protein. Partial amino-terminal sequence analysis showed that the smaller fragment corresponds to the amino-terminal "signal peptide" of f1 pre-coat protein. Cleavage occurred only if the membrane fraction was present during in vitro synthesis, and was not observed if it was added after completion of pre-coat protein synthesis. The cleavage reaction was strongly stimulated when the membrane fraction was present together with the nonionic detergent Nikkol. These results are consistent with and discussed in terms of the signal hyothesis.

Amino Acid Sequence↗
PubMed1977

Interaction of rabbit reticulocyte ribosomes with bacteriophage f1 mRNA and of Escherichia coli ribosomes with rabbit globin mRNA.

We have compared the behavior of a prokaryotic mRNA in a eukaryotic ribosome binding system and of a eukaryotic mRNA in a prokaryotic ribosome binding system. Using (32)P- and (125)I-labeled bacteriophage f1 mRNA, we have shown that rabbit reticulocyte 80S ribosomes can protect specific sequences from pancreatic RNase digestion, including those sequences protected by Escherichia coli ribosomes. We have also found that E. coli ribosomes fail to protect any region of (125)I-labeled globin mRNA. Iodination of the mRNA appeared to have little or no effect on the specificity of binding or protection by the ribosomes of either system.The eukaryotic and prokaryotic systems differ markedly in the ability of the small ribosomal subunits to protect mRNA from nuclease digestion. The regions of phage f1 mRNA protected by E. coli 30S subunits are virtually identical to those protected by the 70S ribosomes. By contrast, rabbit reticulocyte 40S subunits protect substantially larger fragments of mRNA from nuclease digestion than do the 80S ribosomes. These 40S-protected fragments are specific in the case of globin mRNA and overlap the shorter region protected by the 80S ribosomes. However, the 40S-protected fragments of phage f1 mRNA were found to be extremely heterogeneous, reflecting perhaps an important difference between the initial interactions made by these two mRNAs with the ribosomes.

Animals↗