Mapping of Temperature-sensitive Mutants in Bacteriophage T5.

5, one of the classical T phages of Escherichia coli, has been the subject of many studies, but its genetic analysis has been sporadic. Beginning with heatstable ( s t ) mutants (ADAMS and LARK 1950; ADAMS 1953), there have been reports of mutants with altered host range (LANNI and LANNI 1956), serological behavior (LANNI and LANNI 1957), lysis-inhibiting properties (U. T. LANNI 1958), and buoyant density and sedimentation rate (HERTEL, MARCHI and MULLER 1962; LARK 1962). Host-range and serological differences are correlated, as are differences in heat-stability and density. Several of the aforementioned mutants show altered plaque type. Additional plaque-type mutants of various kinds are easily isolated from routine assay plates, especially with E. coli strain F as the host. Genetic recombination in T5 was first reported by ADAMS (1951, 1952) in crosses between T5 and the taxonomically related phages PB. BG3, and 29 alpha. which were independently isolated from natural sources. T5, PB, and their hybrids have been used in studies of the cytological effects of phage infection (MURRAY and WHITFIELD 1953) and the genetic control of host-range and serological specificity ( FODOR and ADAMS 1955; FODOR 195 7; WASSERMANN 1959; see also F. LANNI 1958). The considerable mutual exclusion in mixed infection and the multiple hereditary differences between the parents limit the value of these interstrain crosses for genetic mapping. More recently, HERTEL et al. (1962) reported recombination between plaque-type and density markers in T5 mutants, and NI. NESSON (personal communication from R. S. EDGAR) observed recombination between temperature-sensitive ( t s ) mutants of the kind to be described here. (Note: The st phenotype involves an increased stability of the free phage particle in media of low ionic strength, whereas the ts phenotype involves a decreased ability to grow at a moderately elevated temperature). A suitably comprehensive genetic map is needed in conjunction with studies of T5 progressing in various laboratories and in comparative bacterial virology. For example, under certain well defined conditions the T5 DNA molecule can be sectioned artificially during transfer from the infecting phage particle to the host cell. The transferred section amounts to about 8 percent of the whole DNA