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 λ
cb
2 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 ofλ
cb
2 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.
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