The template of the isolated native simian virus 40 transcriptional complexes is a minichromosome

Abstract

Native simian virus 40 (SV40) transcriptional complexes containing active DNA-dependent RNA polymerase B enzymes that have initiated synthesis in vivo were extracted by salt from nuclei of infected cells late in infection. These complexes can synthesize RNA chains longer than the viral genome under conditions that do not irreversibly alter the structure of the viral chromatin. The RNA synthesized in vitro allowed the separation of most of the viral transcriptional complexes from transcriptionally inactive SV40 minichromosomes. Density studies indicate that about the same amount of protein is associated with both the bulk of the viral minichromosomes and the transcriptional complexes. Parallel shifts in the sedimentation of bulk minichromosomes and transcribing complexes at increasing ionic strength and after nucleosome “exchange” strongly suggest that the actively transcribed viral genome has a structure similar to that of the bulk of viral chromatin. In agreement with the biochemical results, electron microscopy studies strongly suggest that the template for late viral transcription has a minichromosome-like structure.