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Summary: A new temperate phage, R4, of Streptomyces was isolated from soil on a restriction-deficient mutant of S. albus G. In its morphology, adsorption properties and growth kinetics R4 resembled other temperate phages of Streptomyces though its requirements for Ca2+ and Mg2+ were higher than usual. It was unable to form plaques above 34.5°C. R4-mediated transduction was not detected. Unlike other Streptomyces 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, S. coelicolor A3(2)] could be lysogenized.With the wild-type R4, plaques were obtained on S. albus 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 S. albus G (SalGI) and S. albus P (SalPI) systems. R4G mutants, but not R4, were sensitive to a restriction–modification system present in two S. rimosus strains (2251 and NRRL 2234). DNA from SalGI-unmodified (but not from modified) R4 or R4G was cleaved by SalGI into more than 30 fragments (mean size 1.35 kilobases; summed molecular weight 30.02 × 106). R4 DNA was cleaved at one site by EcoRI, at one site by SalPI (.PstI), and not at all by HindIII or BamHI.

A New, Wide Host-range, Temperate Bacteriophage (R4) of Streptomyces and its Interaction with some Restriction-Modification Systems