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During late lytic infection of mouse kidney cell cultures polyoma 16S and 19S (late 19S RNA) were isolated by oligo(dT)-cellulose chromatography. Approximately 60-80% of total cytoplasmic polyoma RNA contained tracts of poly(A) which were retained by oligo(dT)-cellulose. Early in lytic infection when viral DNA synthesis and the production of capsid protein are blocked by the addition of 5-fluorodeoxyuridine, approximately 100% of polyoma "early" 19S RNA was quantitatively retained by oligo(dT)-cellulose indicating the presence of poly(A) tracts on most 19S mRNA molecules. In addition, 2 classes polyoma RNA, synthesized after the onset of cellular RNA synthesis under conditions where DNA synthesis is inhibited with 5-fluorodeoxyuridine, were found to contain tracts of poly(A). These species sedimenting at 16S and 19S in aqueous sucrose density gradients were also quantitatively retained by oligo (dT)-cellulose.

The transition from early to late transcription of SV40 DNA in productively infected BSC-1 cells was analyzed using both inhibitors of DNA replication, and early (Group A) temperature sensitive (ts) mutants of SV40. Late virus specific cytoplasmic RNA sedimenting at 16S in neutral sucrose gradients and complementary to the plus (L) DNA strand of SV40 was detected in cultures infected in the presence of three inhibitors of DNA replication (Ara-C, FdU, and chloroquine), even though the inhibition of viral DNA replication appeared to be essentially complete. After infection with the early SV40 mutant tsA58, no DNA replication was detected at the restrictive temperature (41 degrees C) and no significant late RNA complementary to the plus (L) strand was found, in either the cytoplasm or nuclei of infected cells. These data support the concept that expression of late viral functions requires the initiation of viral DNA synthesis or a functional gene A protein, or both.

Heterogeneous polyoma giant RNA molecules have been isolated by oligo(dT)- cellulose chromatography during the late phase of a lytic cycle of infection of mouse kidney cell cultures. These RNAs have sedimentation coefficients in denaturing Me2SO gradients that are greater than 26S and thus apparently correspond to RNA molecules larger than one strand of polyoma DNA. Approximately 15% of total nuclear polyoma late giant RNAs contained tracts of poly(A) and were retained by oligo(dT)-cellulose. The polyoma late giant RNAs as well as heterogeneous nuclear RNAs (HnRNAs) were found to have a slightly lower sedimentation rate in Me2SO-chloral hydrate density gradients than sedimentation values in sucrose gradients indicated. Even when synthesis of viral DNA and the production of capsid protein are blocked by 5-fluorodeoxyuridine (FdU), 10% of polyoma-specific RNA (as determined by sedimentation analyses under aqueous conditions) was shown to contain tracts of poly(A). In contrast to our findings on polyoma late giant RNA, nuclear polyoma RNA synthesized in the presence of FdU sedimented in denaturing Me2SO-chloral hydrate gradients considerably slower (from 15 to 30S) in relation to HnRNA and ribosomal precursor RNA. The sedimentation pattern in denaturing Me2SO gradients suggest that Py RNA synthesized late in lytic infection in the presence of FdU may be no longer than one transcript of Py DNA.

The "70S-associated" 4S RNA from avian myeloblastosis virus contains transfer RNA, as determined by aminoacylation. The various amino acids esterified, plus the great number of minor bases found in this "70S-associated" 4S RNA indicate that a sizeable fraction, but not all, of this RNA is transfer RNA.

Using a chemical isotope derivative method, we have determined the minor base composition of the "70S-associated" 4S RNA isolated from avian myeloblastosis virus. The minor base composition of this "70S-associated" 4S RNA is strikingly similar to that of the corresponding "free" 4S RNA of the virion. This minor base content, plus the capacity to esterify amino acids, establishes that both of these virion 4S RNA fractions contain transfer RNA. The percentage of minor bases in virion "70S-associated" 4S RNA is, however, much lower than in "free" 4S virion RNA and in myeloblast 4S RNA. The implication is that the "70S-associated" 4S RNA fraction as isolated herein also contains RNA that is not transfer RNA. This latter RNA may represent either degradation products of high molecular weight RNA or indigenous 4S RNA of undetermined function.