Polyoma virus giant RNAs contain tandem repeats of the nucleotide sequence of the entire viral genome.

Abstract

The bulk of late virus-specific RNA synthesized in polyoma virus-infected mouse cells is larger than a single strand of polyoma DNA. The arrangement of viral nucleotide sequences in these giant polyoma RNA was studied by EM of hybrids between purified high MW viral RNA and the HindII-I fragment of polyoma DNA, which contains 91% of the viral genome. Hybrid molecules containing a short single-stranded gap (corresponding to the 9% of viral sequences not present in Hind-II-I), flanked by double-stranded regions, were photographed and measured. The majority of hybrid molecules contained no single-stranded loops or branches, showing that all viral sequences are transcribed contiguously and that no nonviral sequences are present in the RNA. Hybrid molecules, containing RNA up to 3.5 times the genome length, had a repeating structure of single-stranded gaps 8% of genome length interspersed with double-stranded regions 89% of genome length, showing that giant polyoma RNA contain tandem repeats of the nucleotide sequence of the entire viral DNA. A small proportion of hybrid molecules contained single-stranded branches or deletion loops in characteristic positions, indicating that RNA splicing may occur on high MW nuclear polyoma RNA.