Relationship between β converting and γ non-converting corynebacteriophage DNA

Abstract

BACTERIOPHAGE can convert non-toxin producing strains of Corynebacterium diphtheriae to toxinogeny, and the significance of the difference between β-tox⁺ converting corynebacteriophage isolated by Freeman¹ and γ-tox non-converting phage isolated in this laboratory² has been studied sporadically over the past 20 yr. These two phages are serologically related, but are heteroimmune when tested reciprocally against their lysogenic derivatives³. Both phages exhibit similar one-step growth characteristics and patterns of inducibility by ultraviolet light⁴ and are morphologically similar though differing slightly in head and tail measurements⁵. The phages recombine vegetatively, though at a frequency lower than in homoimmune β matings⁶ and also recombine as prophages in tandem double lysogens⁷. It has been shown⁸ that γ non-converting phage probably carries a cryptic tox gene, or part of the gene, as matings between β-tox and γ-tox have yielded tox⁺ recombinants. These data all suggest that there is a high degree of genetic homology between these two phages. To assess this point more directly we have examined DNA heteroduplexes of the phages and DNA fragments produced by various restriction endonucleases. The data show that the two phages are almost identical.