IDENTIFICATION OF THE COMPLEMENTARY DNA STRANDS OF THE COLIPHAGE DELETION MUTANT λdg_{A_J} BY DNA-DNA HYBRIDIZATION

Abstract

Both complementary strands of coliphage mutant λdg_{A_J} DNA, in which almost the entire left arm (genes A to J) is deleted (Fig. 2)., react with guanine-rich ribopolymers and show only marginal separation during centrifugation in the CsCl density gradient. The preparatively isolated "heavy" and "light" fractions of λdg_{A_J} DNA were shown to correspond respectively to the "heavy" (C) strand and the "light" (W) strand of the wild-type λ or λcb₂ DNA. This was ascertained by DNA-DNA hybridization between nonlabeled λdg_{A_J} DNA fractions bound on nitrocellulose filters and ³H-thymidine-labeled, preparatively separated strands ofλcb₂ DNA. This study shows that both strands of λdg_{A_J} DNA have rather similar affinities for guanine-rich ribopolymers, but nevertheless the C strands of λdg_{A_J} DNA contain somewhat more poly G-binding, dC-rich clusters than the W strands. It also provides a general method for identifying the separated strands derived from DNA fragments, obtained either by shearing or by isolation of DNA from appropriate deletion mutants of the phage.