Virulent viruses that attack Escherichia coli and other enterobacteria. The chromosome is contained in a large capsule of protein, and it is injected into the host through a hollow, tubular tail. The T-even viruses (T2, T4, and T6) have heads 80 × 110 nm, while the T-odd phages (T1, T3, T5, and T7) have isometric heads about 60 nm in diameter. T2, T4, and T6 phages differ in the cell wall receptors to which they bind. Their dsDNAs are linear, cyclically permuted, and terminally redundant. The DNA contains 5-hydroxymethylcytosine (q.v.), rather than cytosine. T2 was the first phage to be observed under the electron microscope (1942, Luria and Anderson), and it was utilized in the famous Hershey-Chase experiment (1952). T4, with a genome of 166 kbp, is the best-known of all the T phages. About 300 of its genes have been characterized. Of the 43 phage-encoded proteins, 16 are used in constructing the head and 27 for the tail. T4 was the subject of the classic studies by Benzer (1955), Crick, Brenner et al. (1961), Brenner, Stretton, and Kaplan (1965), and Edgar and Wood (1966). In the T7 phage DNA replication involves a concatenation (q.v.) of multiple head-to-tail copies of the genome. See Chronology, 1949, Hershey and Rotman; 1961, Rubinstein, Thomas, and Hershey; Genome Sizes and Gene Numbers; bacteriophages, cyclically permuted sequences, rII, triplet code T4 RNA ligase, T7 RNA polymerase, virus.
Subjects: Genetics and Genomics.