Molecular comparison of prolate- and isometric-headed bacteriophages of lactococci

Twelve lytic phages that infect lactococci (eight prolate-headed and four isometric-headed phages) were compared via DNA–DNA hybridization, DNA restriction site mapping, genome size estimation, and analysis of virion proteins. Prolate-headed phages carried double-stranded DNA of 21.8 to 23.4 kilobases and showed three major virion proteins in SDS-polyacrylamide gel electrophoresis. Isometric-headed phages carried double-stranded DNA of 28.1 to 30.4 kilobases and showed one major virion protein. The DNA of all phages had cohesive ends. No DNA hybridization was observed between the two phage types. Restriction endonuclease cleavage site mapping of DNA showed similarities between some of the phages.