The genome of bacteriophage T4.

Over the past three decades, bacteriophage T4 has been genetically, biochemically, and structurally characterized to the point where it is now one of the best understood biological systems. T4 is a complex deoxyribonucleic acid (DNA) virus with a genome large enough to accommodate between 160 and 170 "averagesize" genes of 1,000 nucleotide pairs. About 140 T4 genes now have been identified genetically and, to some extent, characterized functionally. The resulting information provides a fairly complete picture of how such a genome is organized and how it programs the process of viral multiplication in a host bacterial cell. This article provides an overview of the organization and function of the T4 genome, as well as a current reference source of information on the individual genes of T4. The number of essential genes defined by amber (am) and temperature-sensitive (ts) mutations has not changed appreciably from the 65 identified in the early studies of Epstein, Edgar, and their collaborators (67), although the functions of these genes continue to become more completely understood (34, 58, 214). However, a considerable number ofnew so-called nonessential genes has been identified and characterized in the past few years. A review prepared in 1973 (214) included 30 of these genes, and the total now has increased to over 70. We have summarized current knowledge on the locations, sizes, and functions ofT4 genes in the form of a detailed linkage map, tables of gene functions, and a chart showing classes of gene functions. To keep the bibliography to a reasonable length, we have not attempted to reference all of the papers from which information has been taken. Instead, wherever possible, we have cited recent research publications or review articles that in our judgment provide the most convenient access to earlier literature. Additional references to original work may be found in several other recent compilations of information on the T4 genome (34, 58, 62, 140, 155a, 214). GENE CLASSES AND GENE NAMES