Comparison of Polyoma Virus Transcription in Productively Infected Mouse Cells and Transformed Rodent Cell Lines

The early region of polyoma virus DNA encodes at least three proteins: large T protein (100K), middle T protein (55K), and small T protein (22K) (Ito et al. 1977; Shaffhausen et al. 1978; Hutchinson et al. 1978; Smart and Ito 1978; for discussion of the early region DNA and its coding functions, see also Soeda et al. 1979a,b; Friedmann et al. 1979). These polypeptides are not encoded by separate DNA sequences. A favored hypothesis to account for the relationships among the three proteins is that they are translated from three similar but differentially spliced mRNAs. In the first part of this paper, we describe the structures of the polyoma virus early mRNAs and demonstrate that they are consistent with this hypothesis.