Polyoma virus early and late mRNAs in productively infected mouse 3T6 cells

Abstract

We mapped polyoma virus-specific mRNAs isolated from productively infected mouse 3T6 cells on the viral genome by analyzing nuclease St-resistant RNA-DNA hybrids. The polyoma early mRNAs, which code for the three T antigens, have several 5' ends near 73 map units (m.u.). During the late phase of infection an additional 5' end is found near 71 m.u. All of the major early mRNAs have common 3' ends at 26.01 m.u. There is a minor species of early mRNA with a 3' end at 99.05 m.u. There are two proximal and two distal splice junctions in the early region which are used to generate three different spliced early mRNAs. There are three late mRNAs encoding the three virion proteins, VP1, VP2, and VP3. The late mRNAs have common 3' ends at 25.34 m.u. The late mRNAs have heterogeneous 5' leader sequences derived from the region between 65.53 and 68.42 m.u. The leader sequences are joined to the bodies of the messages coding for VP2, VP3, and VP1 at 66.59, 59.62, and 48.57 m.u., respectively. These results confirm and extend previous analyses of the fine structure of polyoma mRNAs.

Polyomavirus late pre-mRNA processing: DNA replication-associated changes in leader exon multiplicity suggest a role for leader-to-leader splicing in the early-late switch

“…This switch results in a dramatic change in the relative abundances of Eand L-RNA; by 24 h postinfection, the ratio of E-RNA to L-RNA is about 1:50 (7,22,24,32,36). The switch is dependent on viral DNA replication; if replication is inhibited, E-RNA accumulates to abnormally high levels, with minimal accumulation of L-RNA (12, 14, [21][22][23].…”

Duplication of noncoding sequences in polyomavirus specifically augments the development of thymic tumors in mice

“…Although these sequence elements clearly constitute large T-binding sites in vitro, there has been no report indicating that large T antigen binds to them in vivo. The major early mRNA start site (nucleotide 150) is downstream of the BglI site(s) (1,9). Analysis of the sequence in PTA including the duplication shows that even if possible upstream early start sites are utilized (6,9), no open reading frames with initiating ATG codons are present.…”

“…The major early mRNA start site (nucleotide 150) is downstream of the BglI site(s) (1,9). Analysis of the sequence in PTA including the duplication shows that even if possible upstream early start sites are utilized (6,9), no open reading frames with initiating ATG codons are present. We therefore consider the 40-bp repeat a noncoding sequence with potential regulatory function.…”

“…Singlebase-pair differences are indicated with vertical lines. For reference, the enhancer regions A and B (5,10,11,14), the origin of replication, the major large T antigen-binding sites (2,3), and the early mRNA start site (1,9) are shown. The locations of the restriction enzyme sites for BclI (nucleotide 5021), PvuII (nucleotides 5128 and 5262), and BgII (nucleotide 87) are indicated (13).…”

Polyomavirus late leader region serves an essential spacer function necessary for viability and late gene expression

“…The 5'-nontranslated sequences of polyomavirus late mRNAs are unusually heterogeneous. At least 15 different capped termini map throughout a 125-nucleotide region, from nucleotide 5075 to nucleotide 5168 on the viral genome (5,12,17,42). In addition, late messages contain variable numbers of a reiterated 57-nucleotide late leader sequence (nucleotides 5020 to 5076) at their 5' ends (24,41).…”