Cloned genes for bacteriophage T4 late functions are expressed in Escherichia coli

Using transposon Tn5 insertions to sequence bacteriophage T4 gene 11

A simple and rapid method of creating an overlapping set of deletions in cloned DNA in preparation for sequencing has been developed. The method is based on a positive selection for Tn5 transposition into the cloned DNA fragment on a high-copy-number filamid, resolution of potential filamid dimers by filamentous phage infection, and the use of Tn5 both as a "portable" restriction enzyme site for in vitro DNA deletion and a "portable" sequencing primer binding site to initiate DNA sequencing reactions using a custom primer complementary to the outside ends of IS50. This new method has been utilized to sequence bacteriophage T4 gene 11, encoding the T4 baseplate protein gp11. The coding sequence of gene 11 is 657 bp in length, and predicts a primary structure of 219 amino acids that agrees well with the biochemical data previously obtained. DNA sequence around gene 11 suggests that the expression of genes 10, 11, and 12 of phage T4 are translationally coupled. Plasmids carrying deletions generated using this method have been used to map genetically five amber alleles of gene 11. These amber alleles were sequenced to confirm the proposed reading frame. The five amber alleles actually represent two different mutational changes at either codon 206 or 207, changing these adjacent glutamine codons to amber. The position of these amber alleles lends support to earlier studies identifying the carboxyl terminus of gp11 as essential in the interaction of P11 with baseplate protein P10 (Plishker and Berget, 1984).

Fate of cloned bacteriophage T4 DNA after phage T4 infection of clone-bearing cells

Plasmid pBR322 replication is inhibited after bacteriophage T4 infection. If no T4 DNA had been cloned into this plasmid vector, the kinetics of inhibition are similar to those observed for the inhibition of Escherichia coli chromosomal DNA. However, if T4 DNA has been cloned into pBR322, plasmid DNA synthesis is initially inhibited but then resumes approximately at the time that phage DNA replication begins. The T4 insert-dependent synthesis of pBR322 DNA is not observed if the infecting phage are deleted for the T4 DNA cloned in the plasmid. Thus, this T4 homology-dependent synthesis of plasmid DNA probably reflects recombination between plasmids and infecting phage genomes. However, this recombination-dependent synthesis of pBR322 DNA does not require the T4 gene 46 product, which is essential for T4 generalized recombination. The effect of T4 infection on the degradation of plasmid DNA is also examined. Plasmid DNA degradation, like E. coli chromosomal DNA degradation, occurs in wild-type and denB mutant infections. However, neither plasmid or chromosomal degradation can be detected in denA mutant infections by the method of DNA--DNA hybridization on nitrocellulose filters.

Molecular cloning of the T4 genome: organization and expression of the tail fiber gene cluster 34--38

lambda T4 derivatives that carry T4 tail fiber genes 34-38 have been isolated and characterized by genetic, structural and functional analysis. 32 lambda T4 recombinants were identified by a marker rescue screen of 310 lambda T4 clones generated by restriction of partial cytosine-containing T4 DNA with either HindIII or EcoRI and ligation into appropriately cleaved lambda vectors. These tests defined 15 recombinant classes with respect to the contiguous stretches of genome recovered. Restriction enzyme structural analysis identified 7 HindIII fragments and 7 EcoRI fragments, established a restriction map covering about 11 kb, and indicated the orientation of the DNA inserts within the lambda vectors. The cloned tail fiber genes are expressed efficiently from lambda promoters and complement in vivo T4 phage carrying amber mutations in the tail fiber genes. Polypeptides corresponding to gp34--gp38 have been detected by SDS polyacrylamide gel electrophoresis of 35S-labeled extracts of appropriate lambda T4 recombinant infected UV-treated host cells. The genetic, structural and functional maps of the T4 tail fiber gene cluster have been correlated, and provide a rational approach to genetically directed DNA sequence analysis of genes 34--38 and their mutant variants that affect the assembly, structure and function of the tail fibers.