Abstract
The molecular size of early and late SV40-specific RNA synthesized in productively infected monkey kidney cells was investigated. Labelled RNA extracted from infected cells was fractionated by velocity centrifugation in a sucrose density gradient and then hybridized with excess, unlabelled SV40 DNA. The largest component in preparations of early SV40-specific RNA, which was synthesized in actinomycin D-treated cells, had a molecular weight of approximately 1.2 x 106. Late after infection, the molecular weight of the predominant species of cytoplasmic SV40-specific RNA was about 1.7 x 106. The latter molecular size corresponds to the full transcription of one SV40 DNA strand into a polycistronic messenger RNA. The major portion of nuclear late virus-specific RNA sedimented at 32 to 50s (molecular weight range: 2.3 to 5.7 x 106), indicating that in the nuclei of productively infected cells the virus genome can be transcribed into RNA molecules much larger than a single virus DNA strand.
* Present address: Institute for Research in Mental Retardation, Staten Island, New York, N.Y. 10314.