Transcription of the cellular DNA sequences in a cloned host-substituted SV40 dna variant

Abstract

The transcription of a cloned host-substituted SV40 genome of defined structure was studied in cells coinfected with wild-type virus and in in vitro reactions with Sarkosyl nuclear extracts (transcription complex preparations) of the coinfected cells. Evidence for the transcription of the monkey DNA sequences in substituted SV40 was obtained in both systems. Efforts to detect similar transcripts in uninfected cells, or in cells infected with wild type SV40 alone, were not successful. Both the highly reiterated and nonreiterated types of cellular DNA sequences (which are linked in the genome of the cloned substituted SV40 variant) were transcribed in the coinfected cells and the RNA transcripts were detected in the nuclear and in the cytoplasmic fractions. Relative to the amount of wild-type SV40 RNA, 40% of the RNA synthesized after in vitro incubation of transcription complex preparations, hybridized with substituted SV40 cellular DNA sequences. In contrast, only 15% of the nuclear RNA and 4% of the cytoplasmic RNA from intact cells hybridized with the cellular DNA derived from substituted SV40. The sucrose gradient sedimentation profile of the host-substituted SV40 RNA was uniquely different from and more heterogeneous than that of wild-type SV40 RNA. RNA homologous to the host DNA in the substituted SV40 variant was associated only with lighter (disomal and monosomal) ribosomal fractions.