R plasmid R772 was isolated from a strain of Proteus mirabilis and is a self-transmissible P-1 incompatibility group plasmid having a molecular weight of about 27 x lo6. It renders bacterial hosts resistant to kanamycin. Phage PR772 was isolated as a phage dependent on the presence of R772 in bacterial hosts. It is hexagonal-shaped with a diameter of 53 nm, has a thick inner membrane and no tail. Vaguely defined appendages are sometimes apparent at some vertices and the phage possesses double-stranded DNA. The DNA has a guanine plus cytosine molar content of 48':d. The phage is sensitive to chloroform and has a buoyant density of 1.26 g ~m -~. These observations suggested that the inner membrane of the phage could contain lipid. Phage PR772 differs in morphology from the doublestranded DNA plasmid-specific phages PR4 and PRRl which adsorb to tips and sides, respectively, of sex pili coded for by P-1 incompatibility group plasmids. Phage PR772 formed clear plaques which varied in diameter. Serologically, phages PR772 and PR4 are possibly related though very distantly, but the two phages have identical host ranges. Phage PR772 adsorbed by one of its apices to tips of sex pili coded for by plasmid R772 in Escherichia coli. It also formed plaques on Salmonella typhimurium, Proteus morganii and Providence strains harbouring this plasmid as well as strains of E. coli carrying plasmids of incompatibility groups N or W. The phage produced areas of partial clearing on lawns of P. mirabilis PM5006 harbouring plasmid R772, the P-1 incompatibility group plasmid RP4, the W group plasmid RSa or the N group plasmid N3, and on lawns of Providence strain P29 carrying plasmid RP4.

Phages C-2 and J were isolated from sewage. Phage C-2 was filamentous and formed plaques on Salmonella typhimurium strains carrying various C plasmids. It also plated on Proteus mirabilis and Serratia marcescens strains carrying particular C plasmids, but failed to form plaques on lines of Escherichia coli K12 strains harbouring most of these plasmids, although in all cases, phage multiplication on the strains was demonstrated. No phage increase occurred in any strain which lacked a C plasmid or contained plasmids of other incompatibility groups. The phage was sensitive to chloroform and, unlike other filamentous bacterial viruses, adsorbed to shafts of conjugative pili. It had a disc-like structure at the end which attached to the pilus. Phage C-2 had a buoyant density of 1.30 g cmd3 and a single-stranded circular DNA genome of 3.0 MDal. Phage J had an hexagonal head with an inter-apical distance of 40nm and a short noncontractile tail. It was resistant to chloroform and diethyl ether. The phage formed plaques or propagated on E. coli strains harbouring some IncC plasmids and all IncJ and IncD plasmids tested. The phage did not form plaques but propagated on P. mirabilis and Ser. marcescens strains carrying these plasmids. It did not plate or propagate on S . typhimurium strains harbouring the plasmids. The plaques were very hazy and variable in size. The phage attached sparsely, at a site which appeared to be located at the base of the tail, to sides of conjugative pili.

SUMMARYThe genomes of pilus-specific, lipid-containing phages PR4 and PR772 were studied electron microscopically. An identical mol. wt. of IO-9 × IO ~ was obtained. The genomes are unique (non-permuted) and have cohesive ends. From the similarities in size and denaturation maps of the genomes and failure to demonstrate non-homology in heteroduplexes, reported morphological ambiguities were clarified. The known serological difference between the phages could not be related to non-homology of their genomes. It is concluded that phages PR4 and PR772 are the same phage.

Abstract— –The response of two pyridoxal‐phosphate‐requiring enzymes of E. coli, tryptophanase and tryptophan synthetase, to near UV light (320–400 nm) has been studied. Tryptophanase is inactivated both in vivo and in vitro, but tryptophan synthetase is resistant to near UV under both conditions. This shows that near UV inactivation is not general for pyridoxal‐phosphate‐requiring enzymes. Substrate protection against light inactivation is demonstrated for tryptophanase. It is furthermore shown that pyridoxal phosphate is required for inactivation of this enzyme. However, the action spectrum for this inactivation does not coincide with the absorption spectrum of tryptophanase or of pyridoxal phosphate.