Studies on the mechanism of replication of adenovirus DNA. II. The nature of single-stranded DNA in replicative intermediates.

Replicative intermediates of adenovirus type 5 DNA contain large stretches of single-stranded DNA. We have shown that this single-stranded DNA is mainly of parental origin, whereas all new DNA synthesized during one round of replication has a double-stranded structure. Hybridization experiments of the single-stranded DNA with isolated complementary strands of adenovirus type 5 DNA showed that this DNA hybridized only with the viral L-strand (the strand with the lower equilibrium density in alkaline CsCl) indicating that it represents the viral H-strand. This observation implies that replication always starts from one and the same molecular end. Electron microscopy of partially denatured Y-shaped intermediates confirmed this and showed that replication started from the molecular right end (the end richest in A-T base pairs). In conclusion, we have shown that replication of adenovirus type 5 DNA starts at the molecular right end, displacing the parental H-strand.