From the gut of a slug in your garden you have identified a new circular, double-stranded DNA-containing bacteriophage. Electron micrographs of infected bacteria during production of phage progeny reveal the structures shown below (thick lines represent double-stranded DNA and thin lines represent single-stranded nucleic acids). Alkali treatment of these replicative DNA forms destroys their single-stranded "tails." Bacteria incubated with 15N-nucleosides were infected with this bacteriophage. CsCl equilibrium density centrifugation of DNA (which separates DNA roughly by mass) reveals two bands of phage DNA. The heavier band contains 100 times more DNA than the lighter band.
(a) What is the composition of the single-stranded nucleic acid in the structures shown below?
(b) Suggest a mechanism for DNA replication in this bacteriophage?