Properties of the histones associated with simian virus 40 replicative form nucleoprotein complex

Intracellular forms of simian virus 40 nucleoprotein complexes. III. Study of histone modifications

The modification patterns of histones present in various forms of intracellular simian virus 40 nucleoprotein complexes were analyzed by acetic acid-urea-polyacrylamide gel electrophoresis. The results showed that different viral nucleoprotein complexes contain different histone patterns. Simian virus 40 chromatin, which contains the activities for the synthesis of viral RNA and DNA, exhibits a histone modification pattern similar to that of the host chromatin. However, virion assembly intermediates and mature virions contain highly modified histones. Pulse-chase experiments with [3H]lysine showed that the newly incorporated histones in the virion assembly intermediates were already highly modified. The majority of in vivo acetylation activity of histones occurred on the 70S simian virus 40 chromatin as analyzed by pulse-labeling with [3H]acetate. These results and our previous analysis of the virion assembly pathway suggest that three stages are involved in the packaging of simian virus 40 chromatin into the mature virion: (i) modification of histones, (ii) accumulation of capsid protein around the chromatin with highly modified histones, and (iii) organization of capsid proteins into salt-resistant shells. The role of histone modification in virion assembly is discussed.

Benzo[a]pyrene metabolism in cells productively infected with simian virus 40

The metabolism of benzo[a]pyrene (BP) by cell cultures and cell-free extracts of the monkey kidney cell line CV-1 was studied in uninfected and Simian virus 40 (SV40) infected cells. Metabolites formed were separated by high-pressure liquid chromatography (HPLC) and quantified by liquid scintillation techniques. The profiles metabolites formed by uninfected and SV40 infected cells were similar except that SV40 infected cell cultures metabolized BP at an increased rate relative to uninfected cells. In addition, SV40 infected cell cultures and cell-free extracts produced an unknown compound which eluted between the 3-hydroxybenzo[a]pyrene and BP fractions. This material does not have a retention time characteristic of any of the known metabolites of BP. Labelled BP and/or its metabolites were bound to the viral DNA and histone components of intracellular viral minichromosomes as well as the viral DNA and proteins of mature virions.

Efficient transcription of a compact nucleoprotein complex isolated from purified simian virus 40 virions

Simian virus 40 (SV40) virions were dissociated in vitro by treatment with ethylene glycol-bis-N-N'-tetraacetic acid and dithiothreitol. The compact nucleo-protein core released as a result of the dissociation had a sedimentation value of 110 to 115S compared with a value of 240S for intact virions. The viral cores contained a fraction of the viral proteins VP(1) and VP(2) in addition to the proteins found associated with the viral minichromosome, i.e., VP(3) and histones H(2)A, H(2)B, H(3), and H(4). Our results suggest that the association of VP(1), VP(2), or both with the viral minichromosome, in addition to maintaining a highly compact structure, modifies the transcriptional properties of the nucleoprotein complex. In the presence of saturating amounts of Escherichia coli RNA polymerase, 95 to 100% of the SV40 nucleoprotein cores were able to form transcriptional complexes. Sedimentation analysis of the core transcriptional complex indicated that the initiation and elongation of nascent RNA chains occurred on the compact SV40 core. Cesium chloride density gradient analysis of the SV40 virion core before and after transcription indicated that no substantial loss of protein occurred during the process of transcription. RNA synthesized from SV40 cores was a fairly homogeneous 16 to 18S species with an average chain length of approximately 2,300 nucleotides. Hybridization analysis of this RNA indicated that specific recognition of RNA polymerase promoter sites was preserved, since transcription was asymmetric, occurring preferentially on the "early" SV40 DNA strand. The rate of incorporation of ribonucleoside triphosphates into acid-insoluble RNA with SV40 cores as the template was 70 to 95% of that obtained with supercoiled SV40 form I DNA. SV40 minichromosomes, under identical transcription assay conditions, had an incorporation rate which was 20% of that obtained with SV40 form I DNA. These results show that association of protein VP(1) or VP(2) or both enhances the transcriptional activity and suggest that these "late" viral proteins may play a role in the regulation of expression of the SV40 genome.

Analysis of binding interactions between histone core complex and simian virus 40 DNA. A comparison of acetylated versus non-acetylated histone core complexes

The interactions of acetylated and non-acetylated core complex histones with simian virus 40 (SV40) DNA 1 have been analyzed. A modified filter-binding assay utilizing micrococcal nuclease, which allows quantification of histone octamer binding to DNA has been developed. Using this assay it was determined that both non-acetylated core complex histones ad core complex histones acetylated with acetyl adenylate to levels existing in vivo bind cooperatively to SV40 DNA 1. Although both interactions are cooperative, the magnitude of the cooperativity parameter, omega, is significantly less in the acetylated case. This difference in cooperativity is in contrast to the nearly identical intrinsic association constant, K, observed in both cases.

Isolation and characterization of polyoma uncoating intermediates from the nuclei of infected mouse cells

A method was developed which enabled the efficient recovery of polyoma uncoating intermediates from the nuclei of infected cells at early times after infection (15 min to 12 h). Cells were infected with radiolabeled virus and lysed with the detergent Nonidet P-40. The nuclei were then collected and sonicated, and the products were analyzed on sucrose gradients. The uncoating intermediate sedimented at 190S and was a viral DNA-protein complex closely associated with a structure of host origin. The host material associated with the 190S uncoating intermediate was determined by polyacrylamide gel electrophoresis and visualized by electron microscopy. The amount of 190S uncoating intermediate found in the nucleus increased with time after infection. The viral DNA was predominantly for I. All of the viral proteins were present in the 190S uncoating intermediate in amounts similar to those found in viral DNA-protein complex cores.

Extraction of transcribing SV40 chromosomes in very low salt

SV40 chromosomes capable of continued RNA synthesis in vitro have been extracted from infected cells in solutions of very low ionic strength (5 mM HEPES, 0.25 mM MgCl2). The RNA made is of high molecular weight, and synthesis is sensitive to alpha-amanitin. More RNA is made than from previously described (high salt-extracted) transcription complexes. Transcribing SV40 chromosomes sediment at a rate intermediate between replicating and mature chromosomes, and have a higher ratio of protein to nucleic acid than either. They retain proteins that are lost during exposure to high salt, and might prove valuable in identifying proteins involved in SV40 transcription.