3 Supplement

Abstract

Since the first printing of this book, significant progress has been made in our understanding of the expression of the papovavirus genomes during their lytic cycle. The structures of the stable transcripts of polyoma virus are now known at the nucleotide level. They are summarized in Figures B.3 through B.6 of Appendix B and have been drawn so as to allow direct comparison with the corresponding SV40 RNAs shown in the figures of Appendix A. The availability of recombinant DNA techniques to generate deletion mutants, and of in vitro transcription systems to assess their consequences, has permitted a more precise definition of regulatory sequences in the viral DNAs. Some of this information about the SV40 early promoter and initiation site of DNA replication is summarized in Figure A.6 of Appendix A. The Reference sections of the Appendixes have been enlarged.

In vitro manipulation of SV40 DNA has also shown that an intron is required for the production of stable cytoplasmic mRNA for SV40 capsid protein (VP1). This requirement has subsequently been shown in other eukaryotic systems and may be general for those eukaryotic mRNAs that are normally produced by a splicing mechanism.

The fourth SV40 late protein, whose existence was predicted from the DNA sequence of the virus (Reddy et al. 1978b), has now been detected at very late times during infection. It is encoded by the 5′ leader regions of some of the 16S and 19S late mRNAs. The coding function of these leader sequences may explain the complexity...