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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 singlestranded 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 AT 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.

ReplicatingAd5 DNA was isolated from nuclei of infected KB cells and studied by electron microscopy. Branched as well as unbranched linear intermediates were observed containing extended regions of single-stranded DNA. The relationship between the branched and unbranched structures was studied during synchronized synthesis in the first round of replication after release of hydroxyurea inhibition.The branched intermediates represented early and the unbranched intermediates late stages in the replication cycle. Digestion of the branched intermediates with Eco RI endonuclease revealed that replication had started at the molecular right end (the A-T-rich end). This was confirmed by partial denaturation mapping of branched intermediates. These results confirm and extend a tentative model on the mechanism of Ad5 DNA replication.

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From skin papillomas of the chaffinch (Fringilla coelebs), a virus has been purified and studied by physicochemical techniques and electron microscopy. The virions measure 52 nm in diameter and are composed of 72 morphological units arranged in a skew T ≈ 7d surface lattice. A sedimentation coefficient of about 300S and a buoyant density of 1.34 g/ml in CsCl were determined for the particle. Its protein composition resembles that of human papillomavirus, and the circular double-stranded genome measures 2.6 µm. This is the first demonstration of a member of the Papovaviridae family that affects a non-mammalian host.