Summary: A new temperate phage, R4, of was isolated from soil on a restriction-deficient mutant of G. In its morphology, adsorption properties and growth kinetics R4 resembled other temperate phages of though its requirements for Ca and Mg were higher than usual. It was unable to form plaques above 34.5°C. R4-mediated transduction was not detected. Unlike other temperate phages, R4 had a wide host-range, which correlated better with the absence of detectable class II restriction enzymes than with conventional taxonomic divisions. Many of the sensitive strains [but not, apparently, A3(2)] could be lysogenized.

With the wild-type R4, plaques were obtained on G only after growth on a restriction-deficient, modification-proficient mutant, and then only at a very low efficiency of plating. All of these plaques were of a mutant type (R4G) which (unlike the parental R4 phage) showed conventional patterns of restriction–modification in the G (GI) and P (PI) systems. R4G mutants, but not R4, were sensitive to a restriction–modification system present in two strains (2251 and NRRL 2234). DNA from GI-unmodified (but not from modified) R4 or R4G was cleaved by GI into more than 30 fragments (mean size 1.35 kilobases; summed molecular weight 30.02 × 10). R4 DNA was cleaved at one site by RI, at one site by PI (.I), and not at all by dIII or HI.


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