Viral RNA synthesis and levels of DNA-dependent RNA polymerases during replication of adenovirus 2

RNA Polymerase III as a Gatekeeper to Prevent Severe VZV Infections

In most individuals, varicella zoster virus (VZV) causes varicella upon primary infection and zoster during reactivation. However, in a subset of individuals, VZV may cause severe disease, including encephalitis. Host genetics is believed to be the main determinant of exacerbated disease manifestations. Recent studies have demonstrated that defects in the DNA sensor RNA polymerase III (POL III) confer selective increased susceptibility to VZV infection, thus providing fundamental new insight into VZV immunity. Here we describe the roles of POL III in housekeeping and immune surveillance during VZV infection. We present the latest knowledge on the role of POL III in VZV infection and discuss outstanding questions related to the role of POL III in VZV immunity, and how this insight can be translated into clinical medicine.

Isolation and characterization of monoclonal antibodies directed against subunits of human RNA polymerases I, II, and III

Human nuclei contain three different RNA polymerases: polymerases I, II, and III. Each polymerase is a multi-subunit enzyme with 12-17 subunits. The localization of these subunits is limited by the paucity of antibodies suitable for immunofluorescence. We now describe eight different monoclonal antibodies that react specifically with RPB6 (also known as RPA20, RPB14.4, or RPC20), RPB8 (RPA18, RPB17, or RPC18), RPC32, or RPC39 and which are suitable for such studies. Each antibody detects one specific band in immunoblots of nuclear extracts; each also immunoprecipitates large complexes containing many other subunits. When used for immunofluorescence, antibodies against the subunits shared by all three polymerases (i.e., RPB6, RPB8) gave a few bright foci in nucleoli and nucleoplasm, as well as many fainter nucleoplasmic foci; all the bright foci were generally distinct from speckles containing Sm antigen. Antibodies against the two subunits found only in polymerase III (i.e., RPC32, RPC39) gave a few bright and many faint nucleoplasmic foci, but no nucleolar foci. Growth in two transcriptional inhibitors-5, 6-dichloro-1-beta-d-ribofuranosylbenzimidazole and actinomycin D-led to the redistribution of each subunit in a characteristic manner.

Adenovirus VARNA1 gene B block promoter element sequences required for transcription and for interaction with transcription factors

We constructed mutants with a deletion of either half of the 18 base-pair B block palindrome in the VARNA1 gene, mutants with different intra-palindromic spacings, a complete set of mutants with single base substitutions, and mutants with double and triple base substitutions in the palindrome. The transcription efficiencies of these mutants were determined in human KB cell-free cytoplasmic S100 extracts. The relative competing strength of each mutant, as determined by a sequential competition experiment, was used to assess each mutant's ability to sequester factors into formation of a stable preinitiation complex. The ability of each mutant to assemble transcriptionally active preinitiation complexes was also determined by direct transcription of the isolated complexes. Finally, the ability of each mutant to interact with the transcription factor(s) TFIIIC and form a distinct gel-resolved complex was also determined. From the results of the above assays, we concluded that the two seemingly identical halves of the palindrome did not contribute equally to transcription, or to assembly of the functional preinitiation complex, nor to interaction with TFIIIC. The anterior half (B1) of the B block palindrome, which is proximal to the A block promoter element, played a stronger role in transcription and in assembly of the functional preinitiation complex than the posterior half (B2) of the palindrome. Consistent with this observation, the point mutations in four base-pairs, GTTC, from +60 to +63 in the anterior half of the B block palindrome, has the most severe effect on transcription. In contrast, we showed that the central sequence and the posterior half (B2) played a stronger role than the anterior half (B1) of the B block palindrome in the interaction of the promoter with TFIIIC. This was corroborated by the observation that base substitutions in the central four base-pair sequence of the palindrome, TCGA, from +62 to +65, had the most severe effect on interaction with TFIIIC, and that mutations in most of the sequences in the posterior half of the B block palindrome had more drastic effects than mutations in the anterior half of the palindrome in this interaction. Furthermore, the spacing between the two halves of the B block palindrome had a drastic effect on the overall transcription efficiency and the interaction of the promoter with TFIIIC, suggesting that the interaction between the two halves of the B block palindrome is not only essential, but also synergistic for the interaction with TFIIIC as well as the assembly of a transcriptionally active preinitiation complex and efficient transcription.

A purified adenovirus 289-amino-acid E1A protein activates RNA polymerase III transcription in vitro and alters transcription factor TFIIIC

We have previously demonstrated that a purified bacterially synthesized E1A 289-amino-acid protein is capable of stimulating transcription from the promoters of genes transcribed by RNA polymerase II in vitro (R. Spangler, M. Bruner, B. Dalie, and M. L. Harter, Science 237:1044-1046, 1987). In this study, we show that this protein is also capable of transactivating in vitro the adenovirus virus-associated (VA1) RNA gene transcribed by RNA polymerase III. Pertinent to the transcription of this gene is the rate-limiting component, TFIIIC, which appears to be of two distinct forms in uninfected HeLa cells. The addition of an oligonucleotide containing a TFIIIC binding site to HeLa whole-cell extracts inhibits VA1 transcription by sequestering TFIIIC. However, the addition of purified E1A to extracts previously challenged with the TFIIIC oligonucleotide restores the level of VA1 transcription. When included in the same reaction, an E1A-specific monoclonal antibody reverses the restoration. Incubation of purified E1A with either HeLa cell nuclear or whole-cell extracts alters the DNA-binding properties of TFIIIC as detected by gel shift assays. This alteration does not occur if E1A-specific antibody and E1A protein are added simultaneously to the extract. In contrast, the addition of this antibody to extracts at a later time does not reverse the alteration observed in the TFIIIC binding activities. Never at any time did we note the formation of novel TFIIIC-promoter complexes after the addition of E1A to nuclear extracts. These results clearly establish that E1A mediates its effect on VA1 transcription through TFIIIC in a very rapid yet indirect manner.(ABSTRACT TRUNCATED AT 250 WORDS)

The hepatitis B virus X-gene product trans-activates both RNA polymerase II and III promoters

The transcriptional regulatory activity of the human hepatitis B virus (HBV) X-gene product was investigated. We demonstrate a new property for the HBV X-gene, the strong transcriptional trans-activation of promoters for class III genes. The stimulation of RNA polymerase III (pol III) as well as pol II promoters is shown in cells transiently transfected with the X-gene, and after its stable integration into hepatocytes. We demonstrate that X-gene containing cells stimulate the frequency of pol III transcription initiation by 20- to 40-fold, and accelerate the rate of formation of stable pol III initiation complexes in a manner indistinguishable from that of adenovirus E1a protein. Since the transcription factor TFIIIC has been shown to be limiting in the formation of stable pol III initiation complexes, template commitment experiments were performed which titrate the level of this factor in extracts. We show that X-protein containing extracts are far more efficient in forming stable pol III preinitiation complexes that cannot be competed away upon addition of a second template, indicating that TFIIIC is very probably a target of the X-protein. Thus, the HBV X-protein is apparently a member of a family of trans-activators capable of stimulating both pol II and III promoters, which includes the adenovirus E1a-protein and SV40 t antigen.

Factors responsible for the higher transcriptional activity of extracts of adenovirus-infected cells fractionate with the TATA box transcription factor

Extracts of adenovirus-infected HeLa cells have 5- to 10-fold-higher activity for transcription from the major late promoter in vitro than do extracts of mock-infected or E1A mutant-infected cells (K. Leong and A. J. Berk, Proc. Natl. Acad. Sci. USA 83:5844-5848, 1986). In this study, we analyzed extracts from mock-infected cells and from cells infected with an E1A mutant, pm975, which expresses principally the large E1A protein responsible for the stimulation of transcription. These extracts were fractionated by phosphocellulose chromatography, a procedure which separates factors required for transcription from this promoter (J. D. Dignam, B. S. Shastry, and R. G. Roeder, Methods Enzymol. 101:582-589, 1983), allowing the quantitative assay of individual factors (M. Samuels, A. Fire, and P. A. Sharp, J. Biol. Chem. 257:14419-14427, 1982). Fractions eluted with 0.04, 0.35, and 0.6 M KCl, which contained RNA polymerase II, the upstream factor MLTF, and three general polymerase II transcription factors, had similar activities when prepared from virus-infected or from mock-infected cells. The sequence-specific DNA-binding activity of MLTF was also similar in the virus-infected- and mock-infected-cell extracts. In contrast, the 1.0 M KCl fraction prepared from virus-infected cells consistently exhibited activity severalfold higher than that of the equivalent fraction prepared in parallel from mock-infected cells. E1A protein eluted principally (greater than 80%) in the 0.35 M KCl fraction. Results of others (M. Sawadogo and R. G. Roeder, Cell 43:165-175, 1985) have shown that the 1.0 M KCl fraction, containing 2 to 5% of the unfractionated protein extract, contains a factor which binds specifically to the major late promoter TATA box. These results, together with a recent genetic analysis of the E1B promoter which demonstrated that the TATA box was required for its efficient transcriptional activation (transactivation) by E1A (L. Wu, D. S. E. Rosser, M. Schmidt, and A. J. Berk, Nature (London) 326:512-515, 1987), are consistent with the model that E1A protein indirectly activates the TATA box transcription factor. Consistent with this model was the finding that mutants of the major late promoter containing only the TATA box and cap site region were transcribed at higher rates with extracts from virus-infected cells than with extracts from mock-infected cells. Other models consistent with the results are also discussed.

Factors responsible for the higher transcriptional activity of extracts of adenovirus-infected cells fractionate with the TATA box transcription factor

Extracts of adenovirus-infected HeLa cells have 5- to 10-fold-higher activity for transcription from the major late promoter in vitro than do extracts of mock-infected or E1A mutant-infected cells (K. Leong and A. J. Berk, Proc. Natl. Acad. Sci. USA 83:5844-5848, 1986). In this study, we analyzed extracts from mock-infected cells and from cells infected with an E1A mutant, pm975, which expresses principally the large E1A protein responsible for the stimulation of transcription. These extracts were fractionated by phosphocellulose chromatography, a procedure which separates factors required for transcription from this promoter (J. D. Dignam, B. S. Shastry, and R. G. Roeder, Methods Enzymol. 101:582-589, 1983), allowing the quantitative assay of individual factors (M. Samuels, A. Fire, and P. A. Sharp, J. Biol. Chem. 257:14419-14427, 1982). Fractions eluted with 0.04, 0.35, and 0.6 M KCl, which contained RNA polymerase II, the upstream factor MLTF, and three general polymerase II transcription factors, had similar activities when prepared from virus-infected or from mock-infected cells. The sequence-specific DNA-binding activity of MLTF was also similar in the virus-infected- and mock-infected-cell extracts. In contrast, the 1.0 M KCl fraction prepared from virus-infected cells consistently exhibited activity severalfold higher than that of the equivalent fraction prepared in parallel from mock-infected cells. E1A protein eluted principally (greater than 80%) in the 0.35 M KCl fraction. Results of others (M. Sawadogo and R. G. Roeder, Cell 43:165-175, 1985) have shown that the 1.0 M KCl fraction, containing 2 to 5% of the unfractionated protein extract, contains a factor which binds specifically to the major late promoter TATA box. These results, together with a recent genetic analysis of the E1B promoter which demonstrated that the TATA box was required for its efficient transcriptional activation (transactivation) by E1A (L. Wu, D. S. E. Rosser, M. Schmidt, and A. J. Berk, Nature (London) 326:512-515, 1987), are consistent with the model that E1A protein indirectly activates the TATA box transcription factor. Consistent with this model was the finding that mutants of the major late promoter containing only the TATA box and cap site region were transcribed at higher rates with extracts from virus-infected cells than with extracts from mock-infected cells. Other models consistent with the results are also discussed.

Adenovirus early region 1A protein increases the number of template molecules transcribed in cell-free extracts

Protein encoded by adenovirus early region 1A (E1A) stimulates transcription from adenovirus promoters in vivo. Here we show that this effect can be observed in vitro. In a run-off transcription assay from the adenovirus serotype 2 (Ad2) major late promoter, extracts prepared 20 hr postinfection were 5-15 times more active than mock-infected-cell extracts prepared in parallel. Similar results were observed for in vitro transcription from the protein IX and E3 adenovirus promoters, whereas a 2-fold increase was observed for the human beta-globin promoter. The increased activities of infected-cell extracts did not depend on the expression of viral late proteins or the small E1A-encoded proteins but did require expression of the large E1A protein. These results are consistent with the large E1A protein stimulating transcription in vitro as it does in vivo. By limiting in vitro transcription to one initiation per template, we found that the higher activity of an infected-cell extract was due to an increase in the number of templates transcribed. These results suggest that the large E1A protein either increases the number of active transcription factors in infected cells or facilitates the interaction of cellular transcription factors with promoter DNA.

Functions of and interactions between the A and B blocks in adenovirus type 2-specific VARNA1 gene

The internal transcriptional control region (ITCR) of VARNA1 gene consists of a 33-base-pair (bp) interblock sequence and two 12-bp sequence blocks that are highly conserved in most of the genes transcribed by RNA polymerase III. To define the functions of and study the interactions between the two blocks, we have constructed mutants with altered interblock sequence or spacing for transcription. The results of transcription efficiencies and competing strengths indicated that the interblock sequence was dispensable and the A and B blocks were essential for transcription control. One of the major functions of the interblock sequence was to maintain an optimal spacing for an intimate interaction between the two essential blocks. Shortening or elongating the interblock spacing in the mutants beyond this range drastically decreased the transcription efficiencies and competing strengths of these mutated genes. To further study how the interaction between the two blocks leads to initiation, the start sites and sizes of RNA products of the mutants were determined. When the interblock spacing was less than 105 bp, the wild-type start site was dictated by the A block after an interaction with the B block through proteins. However, when the interblock spacing was longer than 105 bp, several new start sites located closer to the B block were preferentially used. This suggests that new start sites may be dictated by the B block when its interaction with the A block is weakened by longer spacing. The mechanisms of interaction between the bipartite domain in this gene leading to initiation are different from those in tRNAs and Alu-family RNA genes.

Enhancement of RNA polymerase III transcription by the E1A gene product of adenovirus

Nuclear extracts from adenovirus-infected HeLa cells harvested early in infection demonstrated a markedly increased capacity for transcription by RNA polymerase III of exogenous VA RNA genes, as well as cloned tRNA and 5S RNA genes. In contrast, no enhanced transcription was observed in extracts from cells infected with an E1A deletion mutant. Moreover, cells co-transfected with the VA- and E1A-containing plasmids showed markedly higher levels of VA RNA synthesis than did cells transfected with the VA-containing plasmid alone. Although analysis of high ionic strength extracts revealed that the enhancement of pol III transcription persists late in infection, moderate ionic strength extracts indicated that transcription factor IIIC becomes limiting. Chromatographic fractionation and complementation analysis of extracts from mock- and virus-infected cells indicated that the factor(s) responsible for the enhanced activity was localized entirely in the fraction containing transcription factor IIIC.

Effects of adenovirus infection on rRNA synthesis and maturation in HeLa cells

The production of cytoplasmic and nucleolar rRNA species was examined in HeLa cells infected with high multiplicities of adenovirus type 5. Both 28S and 18S rRNA newly synthesized in infected cells ceased to enter the cytoplasm as reported previously (N. Ledinko, Virology 49: 79-89, 1972; H. J. Raskas, D. C. Thomas, and M. Green, Virology 40: 893-902, 1970). However, the effects on 28S cytoplasmic rRNA were observed considerably earlier in the infectious cycle than those on 18S rRNA. The inhibition of cellular protein synthesis and of the appearance in the cytoplasm of labeled cellular mRNA sequences (G. A. Beltz and S. J. Flint, J. Mol. Biol. 131: 353-373, 1979) were also monitored in infected cultures. During the later periods of an infectious cycle, from 18 h after infection, nucleolar rRNA synthesis and processing and exit of 18S rRNA from the nucleus were inhibited, probably reflecting the failure of infected cells to synthesize normal quantities of ribosomal proteins. The earliest responses of cellular RNA metabolism to adenovirus infection were, however, the rapid and apparently coordinate reductions in the levels of newly synthesized 28S rRNA and cellular mRNA sequences entering the cytoplasm.

Effects of adenovirus infection on rRNA synthesis and maturation in HeLa cells

The production of cytoplasmic and nucleolar rRNA species was examined in HeLa cells infected with high multiplicities of adenovirus type 5. Both 28S and 18S rRNA newly synthesized in infected cells ceased to enter the cytoplasm as reported previously (N. Ledinko, Virology 49: 79-89, 1972; H. J. Raskas, D. C. Thomas, and M. Green, Virology 40: 893-902, 1970). However, the effects on 28S cytoplasmic rRNA were observed considerably earlier in the infectious cycle than those on 18S rRNA. The inhibition of cellular protein synthesis and of the appearance in the cytoplasm of labeled cellular mRNA sequences (G. A. Beltz and S. J. Flint, J. Mol. Biol. 131: 353-373, 1979) were also monitored in infected cultures. During the later periods of an infectious cycle, from 18 h after infection, nucleolar rRNA synthesis and processing and exit of 18S rRNA from the nucleus were inhibited, probably reflecting the failure of infected cells to synthesize normal quantities of ribosomal proteins. The earliest responses of cellular RNA metabolism to adenovirus infection were, however, the rapid and apparently coordinate reductions in the levels of newly synthesized 28S rRNA and cellular mRNA sequences entering the cytoplasm.

Human mutant cell lines with altered RNA polymerase II

A human fibrosarcoma cell line, HT-1080-6TG-9AM, resistant to alpha-amanitin at concentrations up to 10 micrograms/ml, was isolated after ethylmethanesulfonate mutagenesis and stepwise selection. The mutation is stable and dominant. RNA polymerase II purified from the mutant cells showed an altered affinity for labeled alpha-amanitin and the sensitivity of the enzyme to the fungal toxin was decreased 50- to 100-fold. This functional test demonstrated that the biochemical basis for the resistance of the cells to alpha-amanitin is due to an alteration of RNA polymerase II.

DNA-dependent RNA polymerase activity in silkmoth-wing epidermis after hormone treatment

DNA-dependent RNA polymerase activity of wing epidermal tissue from the silkmoth, Antheraea polyphemus, has been studied after treatment of pupae with either molting hormone 20-hydroxyecdysone or 20-hydroxyecdysone and juvenile hormone. Enzyme activity has been measured both on endogenous template in isolated nuclei and on exogenous template after solubilization and correlated with transcriptional activity measured as the incorporation of [3H]uridine into RNA. Within 4 h of either hormonal regimen, increases in nuclear transcriptional activity for enzymes I and II are observed. Maximal nuclear activity for both enzyme classes was observed at 26 h. Solubilized enzyme activity, on the other hand, increased continuously up to 144 h. The increase in enzyme activity at 26 h, and probably earlier, is dependent on both RNA and protein synthesis, indicating that the increase is not a consequence of the activation of inactive molecules, but requires the synthesis of either new enzyme molecules or effector molecules. Application of 20-hydroxyecdysone + juvenile hormone does not significantly affect nuclear RNA polymerase activity, rates of RNA synthesis or even RNA content during the first 26 h. However, JH causes significant diminution in the rise of solubilized activity observed with 20-hydroxyecdysone. This reduction is not a consequence of diminished protein content. Therefore, the number of active RNA polymerase molecules appears not to directly correspond to the rate of RNA synthesis.

In vitro transcription of chromatin containing histones hyperacetylated in vivo

The culture of cells in the presence of sodium n-butyrate causes an accumulation of histones that are highly acetylated. When chromatin containing these histones was transcribed with E. coli RNA polymerase, an increase in the template activity compared to control chromatin was observed. Titration of chromatin with polymerase under both reinitiating and non-reinitiating conditions showed there was no increase in the number of regions available for transcription. Comparison of the kinetics for single and multiple rounds of transcription indicated that the rate of elongation was increased and probably the rate of reinitiation as well. Comparison of the size of transcripts from control and acetylated chromatin showed a small increase in the average size of transcripts from acetylated chromatin. When transcription was compared using partially purified HeLa polymerase, an increase was also seen. Studies under various ionic conditions showed that control chromatin required a higher salt concentration for optimum activity than did acetylated chromatin. In addition, at the optimum salt concentration for each chromatin, there was very little difference in the transcriptional activity using exogenous HeLa RNA polymerase.

Characterization of RNA synthesized in isolated nuclei of herpes simplex virus type 1-infected KB cells

Nuclei isolated from herpes simplex virus (HSV)-infected KB cells actively synthesize HSV RNA in vitro; the RNA can be hybridized with HSV DNA or nuclear RNA from HSV-infected cells. Nascent RNA molecules labeled in vivo with 32PO4 were elongated, utilizing the nuclear system to incorporate Hg-CTP at their 3' ends, and then isolated on an affinity column. Hybridization of isolated nascent RNA molecules showed that greater than 50% of them were HSV specific and that more than 25% were self-complementary.

Synthesis and processing of adenoviral RNA in isolated nuclei

Adenoviral RNA sequences synthesized in nuclei isolated during the late phase of productive infection comprise, besides virus-associated, VA, RNA, five major species, ranging in size from approximately 13S to 55S. The latter RNA species is of the length predicted if the major transcriptional unit expressed during the late phase were completely copied in vitro. Some 30% of the RNA sequences labeled in vitro are polyadenylated, and about one-third of the polyadenylated RNA is virus specific. Hybridization analysis of the sequences immediately adjacent to polyadenylic acid in late RNA labeled in isolated nuclei suggests that polyadenylation in vitro occurs at the same sites recognized within the cell. The polyadenylic acid-containing viral RNA sequences made in isolated nuclei are found in three major species of RNA, sedimenting at approximately 28S, 18S, and 13S. These sizes are remarkably similar to those reported for late mRNA species, suggesting that additional processing steps can occur in isolated nuclei. Hybridization of RNA to XhoI fragments of adenovirus type 2 DNA transferred to nitrocellulose filters reveals that sequences complementary to the region from 22.0 to 26.5 units present in 55S RNA are absent from all smaller species, suggesting that the smaller RNA species labeled in isolated nuclei are generated by splicing. The splicing events necessary to generate the 5' leader segment common to the majority of late adenoviral mRNA species are shown to be performed correctly in isolated nuclei.

Transcription of the bovine parvovirus genome in isolated nuclei

Transcription of the genome of the nondefective parvovirus BPV was examined in nuclei isolated from synchronized bovine fetal spleen cells. The relative levels of total RNA polymerase and RNA polymerase I, II, and III activities in nuclei isolated from BPV-infected and mock-infected cells were found to be similar throughout the course of infection. Hybridization of RNA synthesized in isolated nuceli indicated that BPV-specific RNA synthesis began during the period of 8 to 12 h postinfection and proceeded linearly until at least 20 h postinfection. By 20 h postinfection, 5% of the total RNA synthesized in nuclei from infected cells was virus specific. BPV-specific RNA synthesis was inhibited by 95% in the presence of 0.1 microgram of alpha-amanitin per ml, suggesting that the viral genome is transcribed by cellular RNA polymerase II.

Nucleosome-like structural subunits of intranuclear parental adenovirus type 2 DNA

The intranuclear structure of parental adenovirus 2 DNA was studied using digestion with micrococcal nuclease as a probe. When cultures were infected with 32P-labeled virions, at a multiplicity of 3,000 particles per cell, 14 to 21% of parental DNA penetrated the cell and reached the nucleus. Of this parental DNA, 60% could be solubilized by extensive digestion with micrococcal nuclease. The nuclease-resistant fraction contained viral deoxyribonucleoprotein monomers and oligomers. These nucleosome-like structures contained DNA fragments which are integral multiples of a unit-length DNA of approximately 185 base pairs. The monomeric DNA is similar in length to the unit-length DNA contained in cellular nucleosomes. However, the viral oligomers are slightly smaller than their cellular counterparts. DNA-DNA hybridization demonstrated that all segments of the viral genome, including those expressed as mRNA only at late times, are represented in the nucleosomal viral DNA. The amount of early intranuclear viral chromatin was proportional to multiplicity of infection up to multiplicities of 4,000 particles per cell. However, viral transcriptional activity did not increase in direct proportion to the amount of viral chromatin. Maximum accumulation of intranuclear viral chromatin was achieved by 3 h after infection. The intranuclear parental viral chromatin remained resistant to nuclease digestion even at late times in infection, after viral DNA replication had begun.

Autoregulation of adenovirus type 5 early gene expression. III. Transcription studies in isolated nuclei

The rate of adenovirus RNA synthesis was compared in nuclei isolated from cells infected at 40.5 degrees C in the presence of 1-beta-d-arabinofuranosylcytosine with adenovirus 5 or an early temperature-sensitive mutant of adenovirus type 5, H5ts125 (ts125). In nuclei isolated at various times after infection, the maximum amount of virus RNA synthesis occurred at 6 h after infection, after which time virus RNA synthesis declined in nuclei from wild-type infections but remained high in nuclei from ts125 infections. At 12 h after infection, the amount of virus RNA synthesis was 8- to 11-fold higher in nuclei from ts125 infections than in nuclei from wild-type infections. However, the kinetics of virus RNA synthesis in nuclei isolated from both infections were similar. When a ts125-infected culture was shifted to 32 degrees C for 3 h (12 to 15 h after infection) before nucleus isolation, the amount of virus RNA synthesis in the isolated nuclei was reduced to nearly wild-type levels. A pulse-chase experiment showed little difference in degradation rates of virus RNA in isolated nuclei from wild-type and ts125 infections. Hybridization of RNA synthesized in vitro to restriction fragments of adenovirus type 5 DNA was consistent with early virus RNA. These results support the idea that the 72,000-dalton DNA-binding protein encoded by the mutant gene in ts125 can regulate early adenovirus gene expression by inhibiting initiation of transcription of the adenovirus genome.

Transcription in vitro of adenovirus-2 DNA by RNA polymerases class C purified from uninfected and adenovirus-infected HeLa cells

DNA-dependent RNA polymerase class C (or III) has been solubilized from either uninfected or adenovirus-2-infected HeLa cells and purified by chromatography on phosphocellulose, DNA-cellulose, CM-Sephadex and DEAE-Sephadex. The last column separated the enzyme into three forms CI, CII and CIII, which were completely free of RNA polymerases class A and B and of DNase and RNase. The total and the relative amount of these different enzyme C forms did not vary whether purified from uninfected or infected cells. Irrespective of the stage of purification, the three enzyme forms transcribed deproteinized adenovirus-2DNA very efficiently. This transcription was highly sensitive to elevated ionic strength (especially in the presence of Mg2+) and was accompanied by continuous reinitiation as shown by adding poly(rI), a potent inhibitor of initiation. In addition heparin-resistant initiation complexes could be formed at elevated temperature. The RNA synthesized in vitro on deproteinized intact adenovirus-2 DNA by the different forms of RNA polymerase class C, has been characterized. Analysis of the transcripts by gel electrophoresis, RNA self-annealing, hybridization to separated adenovirus-2 DNA strands and to restriction endonuclease (BamHI, HindIII), adenovirus-2 DNA fragments have demonstrated that restriction endonuclease (BamHI, HindIII), adenovirus-2 DNA fragments have demonstrated that the various regions of the adenovirus-2 genome were randomly transcribed. In addition, hybridization of RNA transcripts labelled at their 5' end by either [gamma32P]ATP or [gamma-32P]GTP indicated that not only elongation but also initiation occurred randomly through the entire adenovirus-2 genome, irrespective of the form of the enzyme and of the origin of the cells (normal or infected). The results are discussed in terms of the components which are possibly involved in specific transcription.

Mapping of adenovirus late promoters with nascent mercurated RNA

Nascent RNA molecules were labeled in vivo and elongated in vitro by incubation of the isolated nuclei in the presence of mercurated nucleotides. The RNA molecules initiated and labeled in vivo and elongated in vitro were then selectively purified on a thiopropyl 6-B Sepharose affinity column. The procedure was shown to be free of artifacts since the addition of mercurated nucleotides and the retention on the affinity column is mediated by the endogenous RNA polymerase II (nucleoside triphosphate:RNA nucleotidyltransferase; EC 2.7.7.6), is sensitive to actinomycin D, and is dependent on the presence of all four ribonucleotide triphosphates. This general procedure was applied to the mapping of viral promoters late after adenovirus 2 infection of HeLa cells. RNA purified as described above was hybridized to restriction enzyme fragments attached to nitrocellulose filters. The 5' ends of the nascent RNA chains are located in coordinates 9.5-17 for a rightward transcript, 0-25 for a leftward transcript, and possibly 60-70 for a second rightward transcript. These locations clearly differ from locations of the early promoters and therefore suggest that the transition from early to late functions is controlled at the transcriptional level.

Stimulation of RNA synthesis in isolated nuclei by partially purified preparations of simian virus 40 T-antigen

T-Antigen was partially purified from nuclei of cells transformed by simian virus 40 (SV 40). When nuclei isolated from either rat liver or quiescent hamster cells were preincubated with T-antigen preparations, there was a marked stimulation of RNA synthesis in an in vitro assay, up to 150% above control levels. The stimulation of RNA synthesis was inhibited by hamster antiserum against T-antigen but not by normal hamster serum. When the T-antigen preparations were fractionated on glycerol gradients, the fractions containing complement-fixing activity with antiserum to T-antigen also had the highest stimulatory activity on nuclear RNA synthesis. T-Antigen was also partially purified from nuclei of cells transformed by a temperature-sensitive A mutant of SV40. When preincubated up to 2 hr at 50 degrees, the T-antigen preparation from these temperature-sensitive A mutants was rapidly inactivated, in terms of both complement-fixing activity and ability to stimulate RNA synthesis in isolated rat liver nuclei. Under the same conditions of preincubation, T-antigen preparations from cells transformed by wild-type SV40 maintained their complement-fixing activity and ability to stimulate RNA synthesis. These results suggest that the biological action of T-antigen may be exerted at the level of transcription.

Low molecular weight viral RNAs transcribed by RNA polymerase III during adenovirus 2 infection

Nuclei isolated from human cells productively infected with adenovirus 2 have been shown to synthesize four low molecular weight RNA species which hybridize efficiently to viral DNA. One species corresponds to the 5.5S or VA RNA (Ohe, Weissman, and Cooke, 1969), and is designated V156. The other three species are novel and have been designated V200, V140, V130, since they are approximately 200, 140, and 130 nucleotides in length, respectively. These viral RNAs retain their distinct electrophoretic properties after denaturation with formamide. RNA species with electrophoretic mobilities similar to those of the V200, V156, and V140 RNAs have been found in the cytoplasmic fraction of cells at late times after adenovirus infection. In isolated nuclei, the V200, V156, V140, and V130 RNAs are all synthesized by DNA-dependent RNA polymerase III, since synthesis is sensitive to high but not to low concentrations of alpha-amanitin. The synthesis of these low molecular weight RNAs continues for a prolonged period of time in isolated nuclei, suggesting that reinitiation occurs. Adenovirus 2 DNA fragments obtained by digestion with restriction endonucleases Eco RI and Sma I were used to map the location of the DNA sequences which encode the RNAs. All the low molecular weight RNAs hybridized to a region of the genome between o.18 and 0.38 fractional lengths from the left end of the adenovirus genome, suggesting that the respective DNA sequences are clustered. Other nonviral low molecular weight RNAs are synthesized in nuclei isolated from infected cells. These include the cellular 5S rRNA species which was minitored by its hybridization to purified 5S DNA from Xenopus laevis.