Structure of polyoma virus late nuclear RNA

Abstract

We have investigated the structure of polyoma virus-specific RNA in the nuclei of 3T6 cells late during productive infection, using standard RNA fractionation techniques and adaptations of the S 1 nuclease/gel electrophoresis mapping technique (Berk & Sharp, 1977). Giant, tandemly repeated, short-lived transcripts of the entire circular viral genome predominate; a proportion of these molecules is polyadenylated. The 5′ termini of these molecules are heterogeneous. The majority map in a 200-nucleotide region centred on 67 map units; a single 5′ end maps in the early region at 92.6 map units. The 3′ termini of polyadenylated viral nuclear RNA molecules map at the same position as those of the cytoplasmic messenger RNAs, 24.9 map units. The only defined 3′ end of non-polyadenylated molecules maps at 93.8 map units. Spliced molecules were detectable only in the polyadenylated nuclear RNA fraction. In general, the structure of the giant late viral nuclear RNA is consistent with its serving as precursor to the late viral messenger RNAs, which each possess 5′ leader sequences comprising a variable number of exact tandem repeats of a short sequence unit present only once in the viral DNA.