Species identification and genome mapping of cytoplasmic adenovirus type 2 RNAs synthesized late in infection

Organization of the double-stranded RNA-activated protein kinase DAI and virus-associated VA RNAI in adenovirus-2-infected HeLa cells

We have examined the cellular distribution of the double-stranded RNA-activated protein kinase DAI in adenovirus 2 (Ad2)-infected and uninfected HeLa cells. In uninfected cells DAI was found to be concentrated in the cytoplasm. In addition, DAI was localized in the nucleoli and diffusely distributed throughout the nucleoplasm. Cells treated with alpha-interferon displayed a similar pattern of distribution for DAI. When RNA polymerase I activity was inhibited by the drug actinomycin D, nucleoli segregated and DAI was found to colocalize with the dense fibrillar region of the nucleoli. During mitosis, the distribution of DAI paralleled that of rRNA. In adenovirus-infected cells the localization of DAI was similar to that in uninfected interphase cells. VA RNAI was detected in Ad2-infected cells by 10–14 hours post-infection as fine dots in the nucleoplasm. By 18–24 hours post-infection, VA RNAI appeared in bigger and more abundant dots in the nucleoplasm and the cytoplasm was intensively labeled. Transient expression of the VA RNAI gene in uninfected cells resulted in a similar localization of the RNA. Our results are consistent with a role for DAI and VA RNAI in protein synthesis and suggest that DAI may play an early role in ribosome biogenesis in the nucleolus in addition to its cytoplasmic role in translation.

cis-dominant defect in activation of adenovirus type 5 E1b early RNA synthesis

A cis-dominant mutation in the adjacent E1a gene disrupted the accumulation of adenovirus type 5 E1b mRNA during the early phase of infection. Steady-state levels of cytoplasmic and nuclear E1b RNAs in cells infected with dl312, a strain that lacks the E1a TATA box, cap site, and much of the coding sequence, were reduced 5- to 10-fold even when the E1a activator was provided in trans. The strain was defective for early E1b RNA synthesis but not for E1b RNA made late or during prolonged incubation in the presence of an inhibitor of DNA replication. The defect in E1b RNA synthesis could not be attributed to the E1a promoter sequences missing in dl312 DNA. If the E1a protein-coding region contains cis-acting regulatory sequences, they are not part of the previously mapped E1b transcriptional control region and may represent additional regulatory elements that ensure prompt and efficient E1b expression during the early phase of infection.

Participation of two human cytomegalovirus immediate early gene regions in transcriptional activation of adenovirus promoters

The participation of human cytomegalovirus (HCMV) immediate early genes in the activation of the expression of adenovirus genes in trans (trans-activation) was examined. The initial strategy used was to determine the ability of HCMV genes to complement mutants of adenovirus E1a, an immediate early gene which encodes a trans-activator. The HCMV immediate early gene regions IE1 and IE2 complemented E1a-deficient mutants in three separate assays. IE1 and IE2 substituted for E1a in the synthesis of infectious adenovirus, late adenovirus RNA, and adenovirus DNA. Complementation by the IE2 gene region alone, but not by IE1 alone, was observed using the most discriminating assay, that for late adenovirus RNA synthesis. A role for both HCMV gene regions in positive transcriptional control was indicated by their ability to increase expression of chloramphenicol acetyltransferase (CAT) mediated by the adenovirus E2a promoter. The IE2 region alone activated CAT synthesis but IE1 alone had no detectable activity. Moreover, the activity of both gene regions was about 10-fold higher than that of IE2 alone. These data indicate that efficient complementation of E1a-deficient mutants and trans-activation of adenovirus early promoters involved the participation of both HCMV immediate early gene regions.

A model system for peptide hormone action in differentiation: interleukin 2 induces a B lymphoma to transcribe the J chain gene

Physiological levels of a purified T cell hormone, interleukin 2 (IL-2), were found to stimulate a cloned murine B cell line (BCL1) to secrete pentamer IgM antibody. The peptide hormone acts at the cell surface via specific IL-2 receptors and induces changes in the 5' chromatin of the J chain gene that correlate with its transcription and with the production of the J chain protein required for pentamer IgM assembly. There was no effect of IL-2 on cell proliferation nor on mu heavy chain gene transcription. These results define a specific function for IL-2 in B cell differentiation. In addition, the IL-2/BCL1 system provides a model for examining the mechanism by which signals generated by hormone-receptor interaction are transmitted to the nucleus and regulate gene expression.

Complementation of an adenovirus 5 immediate early mutant by human cytomegalovirus

The initiation of the lytic cycle of adenovirus 5 requires synthesis of a transcriptional activator encoded by the viral early genetic unit, E1a. Mutant viruses lacking E1a are defective. Human cytomegalovirus activated transcription of early adenovirus genes and complemented an E1a- adenovirus mutant in cells permissive for both viruses.

Splice junctions in adenovirus 2 early region 4 mRNAs: multiple splice sites produce 18 to 24 RNAs

We localized the splice junctions in adenovirus 2 early region 4 (E4) mRNAs. Processing of the E4 precursor RNA positioned the donor splice site of the 5' leader sequence adjacent to acceptor sites near the 5' ends of five of the six open reading regions in the E4 transcription unit. Of particular interest among the E4 mRNAs is an extensively spliced class which includes multiple species with sizes ranging from 1.1 to 0.75 kilobases (kb). Purified 1.1- to 0.75-kb mRNAs specified at least 10 polypeptides in vitro. We detected eight acceptor and two donor splice sites utilized in the deletion of the intron from the 3' portion of these mRNAs. E4 RNAs were isolated from the cytoplasm of infected cells at 5, 9, 12, and 18 h after infection. The E4 mRNAs were present throughout infection, but different members of the 1.1- to 0.7-kb class were predominant at each time assayed. Alternate splicing of the 3.0-kb E4 precursor RNA can generate as many as 25 mRNAs that encode at least 16 polypeptides.

The pattern of integration of viral DNA sequences in the adenovirus 5-transformed human cell line 293

The pattern of integrated adenovirus 5 DNA in the adenovirus 5-transformed human cell line 293 was analyzed by DNA blot hybridization. In contrast to a previous report, only sequences from the left end of the genome were detected. The viral DNA was contained in a unique DNA fragment generated by cleavage of 293 DNA with either EcoRI or BamHI, two enzymes which do not cut the integrated viral DNA. Further mapping studies indicated that the integrated sequence was probably colinear with viral DNA. The joining to host cell sequences occurred between viral nucleotide base pairs 1 and 270 (a site for BalI) on one end and 4123 (SmaI site) and 5372 (BalI site) at the other end. The viral DNA was not tandemly repeated. These results suggest that integration of viral sequences into the host genome probably occurred at a single site. If any subsequent duplications of viral DNA took place, then duplication of extensive cellular sequences also must have occurred.

Identification of adenovirus genes that require template replication for expression

The relationship between adenovirus type 2 DNA replication and expression of intermediate stage viral genes was investigated. The 1.03-kilobase mRNA from early region 1b (E1b) and the mRNAs coding for proteins IX and IVa2 were first detected between 6 and 8 h postinfection. Inhibition of viral DNA replication with hydroxyurea prevented expression of the IX and IVa2 mRNAs, but not of the E1b mRNA. Pulse-labeling experiments demonstrated that the block of IX and IVa2 expression in hydroxyurea-treated cells was at the level of transcription. By a series of superinfection experiments, it was determined that the viral and cellular factors present during the late stage of adenovirus infection are insufficient to activate IX gene expression. The viral DNA template must first replicate before IX transcription can begin.

Expression of adenovirus-2 early region 4: assignment of the early region 4 polypeptides to their respective mRNAs, using in vitro translation

Adenovirus-2 early region 4 (E4; map positions 91.3 to 99.1) encodes six 5' and 3' coterminal, differently spliced mRNAs, which are 2.5, 2.1, 1.8, 1.5, 1.2, and 0.8 kilobases (kb) long. Hybridization selection with five cloned viral DNA fragments that hybridize with subsets of E4 mRNAs was used to purify these six mRNAs and a previously unreported 3.0-kb mRNA from virus-infected cells. E4 mRNAs which were purified by hybridization selection with cloned EcoRI fragment C (map positions 89.7 to 100) were also fractionated by size. The purified mRNAs were then translated in rabbit reticulocyte or wheat germ lysate systems. The full complement of E4 mRNAs specified as many as 16 different polypeptides, with molecular weights ranging from 24,000 (24K) to 10K. The most abundant E4 mRNA, which was 2.1 kb long, specified an 11K polypeptide. The 1.5-kb mRNA, which differed from the 2.1-kb mRNA only by deletion of a second intron from the 3' untranslated region, also specified an 11K polypeptide. The second most abundant mRNA, which was 1.8 kb long, and the 1.2-kb mRNA, which had an intron deleted from the 3' untranslated region, specified a 15K polypeptide. This polypeptide was labeled more intensely with [5,6-(3)H]leucine than with [35S]methionine. The 3.0- and 2.5-kb mRNAs specified four polypeptides (24K, 22K, 19K, and 17K). Translation of E4 mRNAs with a mean size of 0.8 kb, which accumulated preferentially in the presence of cycloheximide, yielded at least 10 polypeptides that migrated in polyacrylamide gels with apparent molecular weights ranging from 21,800 to 10,000. On the basis of translation in wheat germ lysates and the distribution of polypeptides encoded by size-fractionated mRNAs, we concluded that the 0.8-kb mRNA size class includes a heterogeneous mixture of mRNAs which are probably formed as the result of utilization of alternate splice acceptor and donor sites during removal of the second intron. Our polypeptide assignments for the 2.1-, 1.8-, 1.5-, and 1.2-kb mRNAs are compatible with locations of two open coding regions in the DNA sequence (Herisse et al., Nucleic Acids Res. 9:4023-4042, 1981). The relationship between the four polypeptides encoded by the 3.0- and 2.5-kb mRNAs and the two open coding regions is discussed. The production of multiple polypeptides from a heterogenous mixture of mRNAs in the 0.8-kb size class is compatible with two large open coding regions in that part of the sequence. Thus, nearly all of the potential coding information in the leftward strand of E4 is expressed in translatable form during infection. Moreover, alternate splicing of the 0.8-kb mRNA size class can produce multiple polypeptides with common amino-terminal and different carboxy-terminal amino acid sequences, which may have the same function but different specificities.

Transcription of adenovirus 5 early region 1b is elevated in permissive cells infected by a mutant with an upstream deletion

Early region 1b (E1b) of adenovirus 5 consists of a single transcription unit that lies from 1,702 to 4,070 nucleotides from the conventional left end of the genome. The effect of mutations that map upstream of E1b on the production of E1b mRNA was examined in vivo with mutants defective in gene functions from the neighboring early region 1a (E1a) transcription unit (499 to 1,632 nucleotides from the left end). These host range mutants replicate in the adenovirus 5-transformed human cell line 293. E1b mRNA accumulation was assayed by DNA-RNA hybridization late after productive infection when the E1b transcripts are abundant in the cytoplasm. Cells infected by wild-type virus, mutant dl311, or mutant hr1. The elevated levels of E1b mRNA were also detected in steady-state nuclear RNA, pulse-labeled polyadenylated nuclear RNA, and pulse-labeled total nuclear RNA. These data indicate that E1b transcription was elevated in human 293 cells infected with dl312. There was no evidence of increases in genomic DNA in dl312-infected cells, suggesting that the rate of transcription may be elevated. When mixed infections with a 10-fold excess of either dl312 or wild-type virus were performed, the phenotype was that of the more abundant genome. This result suggests that the respective phenotypes were cis dominant. The increased rate of transcription can be attributed to cis-active regulatory effects of the deletion of nucleotides 448 to 1,349 in mutant dl312 DNA.

Expression of abbreviated mouse dihydrofolate reductase genes in cultured hamster cells

We have constructed a number of abbreviated dihydrofolate reductase (DHFR) genes by using cloned mouse genomic and cDNA sequences. These genes contain 1.0 kilobase of 5' flanking genomic sequence and varying portions of the 3' non-coding region. Two of the genes contain the first two introns of the DHFR gene; the other three lack introns. Transfection of DHFR-deficient Chinese hamster ovary cells with any of these constructed genes results in cells with the DHFR+ phenotype. Treatment of the transfectants with methotrexate, a folate antagonist, leads to the emergence of methotrexate-resistant colonies which have amplified the transfected genes.

Regulation of integrated adenovirus sequences during adenovirus infection of transformed cells

A human cell line (293) transformed by adenovirus type 5 encodes mRNA's and proteins from the early region 1 (E1) of the viral genome. These products correspond to those synthesized early after adenovirus infection of normal cells. This pattern of expression is different from that observed at later times in the lytic cycle. We have determined whether integrated sequences can undergo the early-late transition during infection of transformed cells. Cultures of 293 cells were infected with mutants of adenovirus type 5 that have deletions in EI genes. In such infections, the integrated sequence complements the deletion mutants so that viral DNA replication, late mRNA and protein synthesis, and viral assembly occur. Because the infecting genomes lack EI sequences, the products synthesized from the integrated DNA could be analyzed. In contrast to the early-late transition that occurs with EI DNA in free viral genomes, the pattern of mRNAs and proteins made from the integrated sequences was restricted to the early pattern. Assuming that the viral sequences in 293 cells have not become altered during the history of the cells, our results suggest that regulation of integrated adenovirus genes may not be determined exclusively by nucleotide sequence recognition. Apparently, during infection certain factors prevent the integrated viral genes from responding to the regulatory signals which control late expression from free EI DNA. The distinction between integrated and free viral sequences might reflect the different fates of viral and host transcripts during the lytic cycle of adenovirus.

Size heterogeneity in the 3' end of dihydrofolate reductase messenger RNAs in mouse cells

We have examined in detail the RNA coding for dihydrofolate reductase (DHFR) in methotrexate-resistant mouse cells. We find four distinct DHFR messengers, ranging in size from 750 to 1600 nucleotides. All four are polyadenylated and polysomal and can be translated in vitro to produce a 21,000 dalton protein co-migrating with purified dihydrofolate reductase on SDS polyacrylamide gels. The major difference in these RNAs is the length of 3' untranslated regions, varying from about 80 nucleotides in the smallest mRNA to about 930 nucleotides in the largest. The RNAs are also present in methotrexate-sensitive murine cells and mouse liver. Multiple DHFR RNAs are found in the poly(A)+ RNA of methotrexate-resistant Chinese hamster ovary cells but are of different molecular weights than the mouse messengers. We discuss these results in terms of the function of 3' untranslated regions of eucaryotic mRNAs and the possible origin and significance of multiple messenger RNAs for a single protein.

Comparison of the nuclear ribonucleoproteins containing the transcripts of adenovirus-2 and HeLa cell dna

A method as devised allowing the preparation of hnRNA-containing ribonucleproteins (hnRNP) frm HeLa cells infected with adenovirus type 2 under conditions where the extraction of viral replication complexes as minimal. Approximately 60% of the RNA from such hnRNP hybridized with adenovirus DNA. The hnRNP from infected cells had the same general characteristics as those from uninfected cells. Their size was heterogeneous (30-260 S) and depended upon that of their RNA. Their CsCl densities were identical (1.39-1.40 g/ml), indicating the same protein:RNA ratio. Their proteins were found in the same molecular weight range, between 25 000 and 200 000. The major proteins of hnRNP from HeLa cells were present in hnRNP from adenovirus-infected cells. As 60% of the cellular RNA was replaced by adenovirus RNA in hnRNP, this in dicated that there was not stringent specificity in the RNA-protein interactions. The relative proportions of the proteins were identifical in both cases, suggesting that the hnRNP assembly was independent of nucleotide sequences at least for the major proteins. The hnRNP from infected and uninfected cells differed by the size of their RNA, which was larger after infection, and by the presence of six additional minor polypeptides after infection. However, it cannot be excluded that the presence of these polypeptides in hnRNP resulted from non-specific adsorption.

Four sizes of transcript produced by a single sea urchin gene expressed in early embryos

This report concerns a set of sea urchin egg and embryo transcripts complementary to a single-copy region of a cloned DNA fragment (Sp88). Three distinct 16-cell embryo polysomal RNA species were found to hybridize with this fragment. These RNAs are about 1700, 3000, and 4000 nucleotides (nt) in length, and the same species were identified in unfertilized eggs. A significant fraction of all three species of the egg and early embryo transcripts is polyadenylylated. At gastrula stage Sp88 transcripts are almost completely confined to the nucleus [Lev, Z., Thomas, T. L., Lee, A. S., Angerer, R. C., Britten, R. J. & Davidson, E. H. (1980) Dev. Biol, 75, in press]. The Sp88 transcripts of gastrulae are present as a fourth RNA species approximately 5800 nt in length. The four species share a sequence element of cloned DNA fragment that is about 1000 nt long. These RNAs constitute a set of alternative partially overlapping transcripts from the same genomic region.

pMB9 plasmids bearing the Salmonella typhimurium his operon and gnd gene

A plasmid containing the entire Salmonella typhimurium his operon was constructed from plasmid pM89 and an EcoRI fragment of phi 80 his imm lambda DNA. The recombinant pST41 also includes the glucose 6-phosphate dehydrogenase (gnd) gene and has one EcoRI endonuclease cleavage site in the integrated fragment. This plasmid served as a source for the construction of two additional plasmids, one carrying the OGDC-region of the his operon and the other a CBHAFIE segment of the his gene along with the gnd gene. The presence of the his operon in the constructed plasmids was confirmed by hybridization to S. typhimurium his RNA. The location of the gnd gene in the CBHAFIE fragment of the his gene was confirmed genetically: after transfection with the plasmid bearing the gnd gene, a gnd recipient gained the capacity to utilize gluconate as a sole carbon source. The DNAs of the three hybrid plasmids were analyzed by gel electrophoresis. By comparing the EcoRI endonuclease cleavage pattern of these three hybrid plasmids with the DNA cleavage pattern of phi 80 his imm lambda, phi 80 imm lambda and lambda phages, the EcoRI cleavage map of phi 80 his imm lambda was obtained.

In vitro translation products specified by the transforming region of adenovirus type 2

Region 1 DNA sequences (map positions 0 to 11% on the linear adenovirus 2 genome) are expressed both early and late in lytic infection and are required for transformation by the virus. During productive infection six distinct cytoplasmic RNAs are synthesized from this region. These RNAs comprise two families, each consisting of three size classes that share 3' sequences. Region 1 RNA's were purified by hybridization selection, using restriction fragments bound to nitrocellulose membranes, and by size fractionation. The isolated RNAs were then translated in cell-free systems derived from wheat germ and rabbit reticulocytes. The family of RNAs specified by 0 to 4.4 sequences includes two RNAs, which are 12S and 13S in size. These RNAs were partially separated by molecular weight and translated. The 13S RNA produced 53,000-dalton (53K) and 41K peptides, and the 12S RNA synthesized 47K and 35K products. The family of RNAs mapping from 4.4 to 11.0 encodes three separate polypeptides, each of which can be assigned to a specific RNA. A 12K product that comigrates with structural polypeptide IX is synthesized from the 9S RNA as previously reported (U. Pettersson and M. B. Mathews, Cell 12:741-750, 1977). The 13S RNA encodes a 15K polypeptide that corresponds to a 15K polypeptide in infected cell extracts. The 22s RNA encodes a 52K protein distinct from the 0 to 4.4 polypeptides.

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.

Purification of specific adenovirus 2 RNAs by preparative hybridization and selective thermal elution

A method is described for the preparation isolation of highly purified adenovirus RNA species. Cytoplasmic RNAs from cells infected with adenovirus 2 were selected by hybridization to viral DNA fragments bound to nitrocellulose membranes. A series of washes at elevated temperatures (50-70 degrees) determined conditions at which the true hybrids were stable but non-specific RNA was removed. This temperature has been found to correlate with the base composition of the DNA fragment. After washing at this predetermined temperature, the specific RNA was eluted at 85 degrees. The purity of the eluted RNA was greater than 95% as determined by size, sequence specificity, and template activity in an in vitro protein synthesizing system. The method described should be generally useful for purification of specific RNAs.

Parental adenovirus type 2 genomes recovered early or late in infection possess terminal proteins

At both early (3 h) and late (18 h) times after infection of KB cells with adenovirus 2, more than 90% of parental nuclear viral genomes exist as complexes which contain terminally linked proteins. Density shift experiments employing 5-bromo-2'-deoxyuridine indicate that these parental DNA molecules remain complexed with terminal proteins after DNA replication. The persistent linkage of proteins to the termini of intranuclear viral DNA suggests that these proteins have an essential role in adenovirus replication.

Group and type antigens of Capnocytophaga

Group-specific and type-specific antigens have been identified and purified from sonic extracts of Capnocytophaga. The group-specific antigen, which was purified by affinity chromatography, was found to be identical to an antigen present in all 26 strains tested. The antigen is sensitive to trypsin, sodium dodecyl sulfate and heat labile, and composed predominantly (55%) of protein. The type-specific antigen, which was obtained by preparative immunoelectrophoresis, was found to be present in only 3 of the 26 strains tested. This antigen was resistant to heat, trypsin, and sodium dodecyl sulfate and was primarily composed of carbohydrate (47% phenol-sulfuric acid-positive material, 8% amino sugar). Agglutination and fluorescent antibody data suggest that both the group- and type-specific antigens reside on the cell surface.

The spliced structures of adenovirus 2 fiber message and the other late mRNAs

All late adenovirus 2 messenger RNAs, except perhaps that for peptide IX, are composite molecules with sequences derived from at least two to five or more separate portions of the genome, as determined by electron microscopic analyses of polysomal RNA hybridized to single- or double-stranded DNA. We previously reported that eight different rightward-transcribed mRNAs contain, at their 5' ends, a common three-part leader sequence derived from coordinates 16.6, 19.6 and 26.6, and that a ninth mRNA consists of sequences from 4.6--6.1 linked directly to those from 9.7--11.0 (Chow et al., 1977a; revised coordinates). We now demonstrate that four additional RNA species also have the same tripartite leader joined to messages with 5' ends located at coordinates at 29.1, 30.5, 33.9 and 42.8. The RNA transcript extending from 29.1--39.0 covers most or all of the viral associated (VA) RNA genes (29.0--30.1). The late RNAs can be grouped into several families of transcripts in which two or three mRNAs have the same 3' end and 3' proximal sequences, but differ substantially in length at the 5' end and, therefore, the coordinate at which the leader sequences are attached to the main body of the message. The number of RNA species transcribed from the Ad2 chromosome between coordinates 29 and 50 exceeds the number of identified Ad2 proteins. Several pairs of messages differing in length by a few percent may thus encode the same protein or have a precursor-product relationship. We have also found that a subpopulation of the polysomal mRNAs for the fiber protein, the most distal gene (86.3--91.2) in the rightward transcription unit, has a fourth leader component "y" (78.6--79.1) in addition to the common tripartite leader sequences. Less frequent fiber RNA species have fifth "x" (76.9--77.3) and/or sixth "z" (84.7--85.1) leader segments. Transcripts with x, y or z segments might be processing intermediates, and it is possible to arrange these species into an array suggestive of multiple pathways for the maturation of fiber mRNA. mRNA transcribed at late times from the L strand between coordinates 15.0 and 11.0 has a single component leader located 200 bases from the main body of the gene from coordinate 16.1 to 15.7. This leader originates from a site very close to the first leader component (16.5--16.6) of the R strand messages and suggests the presence of adjacent L and R strand promoters from which transcription diverges. Taken together, these results emphasize the diversity of splicing patterns and the variety of recombined sequences generated during the synthesis of late Ad2 mRNAs.

Groups of adenovirus type 2 mRNA's derived from a large primary transcript: probable nuclear origin and possible common 3' ends

Late in adenovirus type 2 infection, a number of mRNA's apparently arise by processing a large nuclear transcript that represents the right-hand 85% of the genome (summarized in Evans et al., Cell 12:733-739, 1977). Hybridization of labeled late mRNA to a series of DNA restriction fragments representing the right-hand 70% of the genome demonstrates at least 12 discrete mRNA's that appear to fall into five groups, each possibly containing a common 3' terminus. The processing necessary to generate these mRNA's apparently occurs in the nucleus. All the mRNA's appear to contain a sequence of approximately 100 nucleotides complementary to a fragment with coordinates 25.5-27.9. This fragment contains one of the regions found by Berget et al. (Proc. Natl. Sci. U.S.A. 74:3171-3175, 1977), Chow et al. (Cell 12:1-18, 1977), and Klessig (Cell 12:9-22, 1977) to the "spliced" onto the 5' end of late adenovirus type 2 mRNA's. Because the sequences to be spliced exist only once per large transcript, any of the mRNA-specific regions might only be preserved from a small fraction of the transcripts. Measurement of the transport efficiency of regions of the large nuclear transcript, if fact, shows that only 15 to 25% of any particular region is transported to the cytoplasm. The overall conclusion of these experiments is that the large late nuclear transcript can be processed in the nucleus to yield any one of many (approximately 12) mRNA's; the unused portions of the primary transcript then accumulate in the nucleus or are destroyed.

Adenovirus type 2 late mRNA's: structural evidence for 3'-coterminal species

Adenovirus type 2-infected HeLa cells were labeled with 32PO4 during the period 14 to 17 h postinfection. Viral mRNA's with polyadenylic acid were isolated by polyuridylic acid Sepharose chromatography and fractionated according to size by electrophoresis through an acrylamide-agarose slab gel. Messenger bands were eluted and partially degraded with alkali. RNA fragments from each band that contain polyadenylic acid were isolated by polyuridylic acid Sepharose chromatography and fingerprinted two-dimensionally after T1 RNase digestion. Three bands, with mobilities of approximately 26S, 21S, and 18S, shared two large characteristic T1 oligonucleotides in common in the fingerprints of their 3'-terminal sequences. These oligonucleotides were mapped with a Hpa II restriction fragment of adenovirus type 2 DNA with coordinates 49-50.2. We conclude that the three mRNA's are coterminal in sequence at their 3' ends and overlap at internal positions. Implications for the protein-coding potential of these mRNA's and the mechanisms of adenovirus tyep 2 late RNA processing are discussed.

Two regions of the adenovirus 2 genome specify families of late polysomal RNAs containing common sequences

Late cytoplasmic RNAs specified by two regions of the adenovirus 2 genome (39.3--51.8 and 70.7--83.4 map units) were analyzed by size fractionation of poly(A)-[3H]RNA and subsequent hybridization to DNA fragments. Both regions encode RNAs whose sequence content exceeds the coding capacity of the region. These multiple transcripts are likely to function as mRNAs, because they are present on polyribosomes. The DNA segment 39.3--51.8 specifies 27S, 22S, and 18S RNAs. The genome sites specifying these three size classes were determined by hybridizations with seven different DNA fragments from this region of the genome. The 3' termini of all three size classes are specified by sequences near a common site, position 50.1. The 27S RNA includes sequences beginning near 39.3, the 22S RNA contains sequences from 41.0, and the 18S RNA includes sequences from approximately 45.3 on the unit genome. A second family of four RNAs is transcribed from 70.7--83.4. These 28S, 22S, 18S, and 16S RNAs have a relationship similar to the RNAs transcribed from 39.3--51.8. Sequences near the 5' ends of these four size classes are specified by different genome sites. However, the 3' termini of all four size classes were localized near map position 80.4. The synthesis of families of RNA may allow the translation of multiple polypeptides from a genome segment that has only one terminator site for mRNA synthesis.

Effect of protein synthesis inhibitors on viral mRNA's synthesized early in adenovirus type 2 infection

Viral mRNA species synthesized early in adenovirus type 2 infection in the presence of cycloheximide were compared with those synthesized in the absence of drug or in the presence of the DNA synthesis inhibitor 1-beta-D-arabinofuranosylcytosine. Cycloheximide caused approximately a 10-fold stimulation in the accumulation of [3H]uridine into early viral mRNA species. The only exception was a 24s mRNA transcribed from the transforming end of the genome; in the presence of cycloheximide, accumulation of this mRNA species was stimulated no more than 2-fold. Treatment with cycloheximide also resulted in the accumulation of polyadenylated RNAs transcribed from EcoRI-C that are heterogeneous and smaller than the 20S mRNA. Other translation inhibitors were shown to have similar effects, suggesting that inhibition of protein synthesis early after infection induces alterations in the metabolism of specific RNA sequences.