T1 pip: a mutant which affects packaging initiation and processive packaging of T1 DNA

The genome and proteome of coliphage T1

The genome of enterobacterial phage T1 has been sequenced, revealing that its 50.7-kb terminally redundant, circularly permuted sequence contains 48,836 bp of nonredundant nucleotides. Seventy-seven open reading frames (ORFs) were identified, with a high percentage of small genes located at the termini of the genomes displaying no homology to existing phage or prophage proteins. Of the genes showing homologs (47%), we identified those involved in host DNA degradation (three endonucleases) and T1 replication (DNA helicase, primase, and single-stranded DNA-binding proteins) and recombination (RecE and Erf homologs). While the tail genes showed homology to those from temperate coliphage N15, the capsid biosynthetic genes were unique. Phage proteins were resolved by 2D gel electrophoresis, and mass spectrometry was used to identify several of the spots including the major head, portal, and tail proteins, thus verifying the annotation.

Molecular genetic analysis of bacteriophage P22 gene 3 product, a protein involved in the initiation of headful DNA packaging

Bacteriophage P22 DNA packaging events occur in processive series on concatemeric phage DNA molecules. At the point where such series initiate, the DNA is recognized at a site called pac, and most molecular left ends are generated within six short regions called end sites, which are present in a 120 base-pair region surrounding the pac site. The bacteriophage P22 genes 2 and 3 proteins are required for successful generation of these ends and DNA packaging during progeny virion assembly. Mutants lacking the 162-amino-acid gene 3 protein replicate DNA and assemble functional procapsids. In this report we describe the nucleotide changes and DNA packaging phenotypes of a number of missense mutations of gene 3, which give the phage a higher than normal frequency of generalized transduction. In cells infected by these mutants, more packaging events initiate on the host chromosome than in wild-type infections, so the mutations are thought to affect the specificity of packaging initiation. In addition to having this phenotype, these mutations affect the process of phage DNA packaging in detectable ways. They may: (1) alter the target site specificity for packaging; (2) make target site recognition more promiscuous; (3) affect end site utilization; (4) alter the pac site; and (5) cause apparent random DNA packaging series initiation on phage DNA.

Transcription stimulates recombination. II. Generalized transduction of Escherichia coli by phages T1 and T4

Phage Mu was inserted in the trpE gene of one donor Escherichia coli strain and in the lac promoter of another. Strains with Mu prophage mutations which permitted transcription of genes whose transcription had been polarly blocked by the Mu insertion were isolated and called "bypass" strains. The transducing phages T1am, and T1am,ST, and, in one instance, T4GT7 were grown on both the bypass and the original strains. After growth on the bypass strains transducing phages were able to transduce Trp+ and Lac+, respectively, to a variety of Trp- and Lac- strains more efficiently than after growth on nonbypass strains. These results support the idea that crossovers required for generalized transduction occur more efficiently if the specific region is transcribed by both interacting parental molecules.