IDENTIFICATION OF THE COMPLEMENTARY DNA STRANDS OF THE COLIPHAGE DELETION MUTANT λdgA_J BY DNA-DNA HYBRIDIZATION

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Abstract
Both complementary strands of coliphage mutant [lambda]dgA-J DNA, in which almost the entire left arm (genes A - J) is deleted, 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 [lambda]dgA-J DNA correspond respectively to the "heavy" (C) strand and the "light" (W) strand of the wild-type [lambda] or [lambda]cb2 DNA. This was ascertained by DNA-DNA hybridization between nonlabeled [lambda]dgA-J DNA fractions bound on nitrocellulose filters and 3H-thymidine-labeled, preparatively separated strands of [lambda]cb2 DNA. This study shows that both strands of [lambda]dgA-J DNA have rather similar affinities for guanine-rich ribopolymers, but nevertheless the C strands of [lambda]dgA-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.