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

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.

Enhanced expression of adenovirus transforming proteins

Proteins encoded in regions EIA and EIB of human adenoviruses cause transformation of rodent cells. One protein from EIA also stimulates transcription of other early regions at early times in a productive infection. In the past, direct analysis of these proteins synthesized in vivo has been difficult because of the low levels produced in both transformed cells and productively infected cells. We present a simple method which leads to expression of EIA and EIB mRNAs and proteins at 30-fold greater levels than those observed during the early phase of a standard productive infection. Under these conditions, these proteins are among the most prominent translation products of infected cells. This allowed direct visualization of EIA and EIB proteins on two-dimensional gels of pulse-labeled total cell protein. Experiments with EIA and EIB mutants confirm that the identified proteins are indeed encoded in these regions. Two EIA proteins are observed, one translated from each of the major early EIA mRNAs. Both of these EIA proteins are phosphorylated.

Mapping of an adenovirus function involved in the inhibition of DNA degradation

A function involved in the inhibition of DNA degradation has been assigned through complementation tests to a product of region E1b of the adenovirus genome (between 4.5 and 10.5 map units). DNA degradation induced by the adenovirus type 12 (Ad12) cyt mutant H12cyt70 and the Ad5 early deletion mutant dl313 (with the deletion between 3.5 and 10.7 map units) was inhibited by coinfection with Ad5 region E1a (between 0 and 4.5 map units) mutants dl312 and hr1 and region E1b mutant hr6. The defect of inhibition of DNA degradation in Ad5 dl313 was also complemented in 293 cells. This DNase-inhibitory function does not appear to involve polypeptide IX or the 58,000-dalton polypeptide. Wild-type Ad12 induced DNA degradation in hamster embryo cells, suggesting that the DNase-inhibitory function is not expressed in these nonpermissive cells. Additional evidence suggests the involvement of a second viral product which positively influences the DNase activity and which appears to be an early function.

Purification of a native membrane-associated adenovirus tumor antigen

A 15,000-dalton protein was purified from HeLa cells infected with adenovirus type 2. Proteins solubilized from a membrane fraction of lytically infected cells was used as the starting material for purification. Subsequent purification steps involved lentil-lectin, phosphocellulose, hydroxyapatite, DEAE-cellulose, and aminohexyl-Sepharose chromatographies. A monospecific antiserum, raised against the purified protein, immunoprecipitated a 15,000-dalton protein encoded in early-region E1B (E1B/15K protein) of the adenovirus type 2 DNA. Tryptic finger print analysis revealed that the purified protein was identical to the E1B/15K protein encoded in the transforming part of the viral genome. The antiserum immunoprecipitated the E1B/15K protein from a variety of viral transformed cell lines isolated from humans, rats, or hamsters. The E1B/15K protein was associated with the membrane fraction of both lytically and virus-transformed cell lines and could only be released by detergent treatment. Furthermore, a 11,000- to 12,000-dalton protein that could be precipitated with the anti-E1B/15K serum was recovered from membranes treated with trypsin or proteinase K, suggesting that a major part of the E1B/15K protein is protected in membrane vesicles. Translation of early viral mRNA in a cell-free system, supplemented with rough microsomes, showed that this protein was associated with the membrane fraction also in vitro.

Expression of the gene encoding the adenovirus DNA terminal protein precursor in productively infected and transformed cells

The major product of in vitro translation of early RNA prepared from H5ts125-infected cells and selected by hybridization to adenoviral DNA fragments spanning the region from 14.7 to 31.5 map units had been shown to be identical to the 87-kilodalton terminal protein precursor. A 72- to 75-kilodalton polypeptide whose rRNA can be selected by DNA from this same region and made in the presence of anisomycin was indistinguishable from the 72-kilodalton single-stranded DNA-binding protein encoded by the region from 60.1 to 66.6 map units. The accumulation of cytoplasmic RNA sequences complementary to these l-strand genes under various conditions of infection and in certain lines of transformed cells has been investigated by solution hybridization of cytoplasmic RNA to the separated strands of restriction endonuclease fragments of adenoviral DNA. During the early phase, RNA sequences complementary to the region from 11.6 to 36.7 map units were present at a concentration of 10 to 60 copies per cell, regardless of the nature of the block used to inhibit viral DNA synthesis. By 24 h after infection in the absence of any such block, sequences complementary to the regions from 11.6 to 18.2 map units (IVa2) and from 18.6 to 36.7 map units (E2B) accumulated to concentrations of 4,800 and 280 copies per cell, respectively. The ratio of cytoplasmic E2A RNA sequences to E2B RNA sequences remained close to 10:1 throughout the time period investigated. Of the transformed cell lines which retained E2B DNA sequences that were examined, only the T2C4 line expressed these sequences in cytoplasmic RNA. The implications of these observations for regulation of expression of the adenoviral early l-strand genes are discussed.

The TATA homology and the mRNA 5' untranslated sequence are not required for expression of essential adenovirus E1A functions

Adenovirus E1A encodes a protein that facilitates the transcription of other early viral transcriptional units and is required for virus-induced transformation. To study the function of non-protein-coding DNA sequence at the 5' end of this transcriptional unit, we constructed mutant viruses with deletions in this region. Deletion of sequence just upstream from the TATA homology does not affect the level or sequence of E1A mRNAs. Deletion of the TATA homology decreases the level of E1A mRNAs by a factor of 5-10 and shifts the mRNA 5' ends from the major 5' end found in wild-type transcripts to a set of minor ends found in wild-type E1A mRNAs. This suggests that the TATA homology is required for an efficient transcription initiation mechanism, and that in its absence a less efficient, less precise mechanism is unmasked. Analysis of mRNAs from other early regions establishes that E2 and E3 regions are most dependent on E1A functions for expression of maximal mRNA levels, E4 is less dependent and E1B is the least dependent. Deletion of the TATA homology, a sequence highly conserved among human adenoviruses, and the entire 5' untranslated sequence of the E1A mRNAs decreases neither the rate of virus replication in a host in which E1A expression is required, nor the efficiency of transformation of rat embryo cells.

Identification and purification of a protein encoded by the human adenovirus type 2 transforming region

The human adenovirus type 2 (Ad2) transforming genes are located in early regions E1a (map position 1.3 to 4.5) and E1b (map position 4.6 to 11.2). We have identified and purified to near homogeneity a major 20,000-molecular-weight (20K) protein and have shown that it is coded by E1b. Using an Ad2-transformed cell antiserum which contained antibody to E1b-coded proteins, we immunoprecipitated 53K and 19K proteins from the nucleoplasm and 53K, 19K, and 20K proteins from the cytoplasmic S-100 fraction of Ad2 productively infected and Ad2-transformed cells. The 19K protein was present in both the nucleoplasm and the cytoplasm, whereas the 20K protein was found only in the cytoplasm. The 53K and 19K proteins are known Ad2 E1b-coded proteins. The 20K protein was purified to near homogeneity in 20 to 50% yields by sequential DEAE-Sephacel chromatography and reverse-phase high-performance liquid chromatography. Purified 20K protein shares most of its methionine-labeled tryptic peptides with E1b-53K, as shown by reverse-phase high-performance liquid chromatography, and therefore is closely related to the 53K protein. The 19K protein does not appear to share tryptic peptides with either 20K or 53K protein. To provide more direct evidence that 20K protein is virus-coded, we translated E1b-specific mRNA in vitro. Both immunoprecipitation analysis and high-performance liquid chromatography purification of the translated product identified a 20K protein that has the same tryptic peptides as the 20K protein isolated from infected and from transformed cells. These findings suggest that the Ad2 20K protein is a primary translation product of an Ad2 E1b mRNA.

Transformation-deficient adenovirus mutant defective in expression of region 1A but not region 1B

A adenovirus type 5 host range mutant (hr440) has been isolated which is defective in a splicing event required to generate the middle-sized mRNA from early region 1A. This defect has been ascribed to two adjacent nucleotide changes which lie five and six nucleotides from the 5' splice site for this mRNA (Solnick, Nature 291:508-510, 1981). One of these changes introduces an amber codon into the reading frame of the largest region 1A mRNA, resulting in the production of a truncated polypeptide. Like other region 1A mutants, hr440 is defective in the production of mRNA from early regions 2 and 3, but hr440 is unusual in that transcription from regions 1B and 4 is normal. Furthermore, although region 1B expression is unaffected, hr440 does not transform baby rat kidney cells. Therefore, expression of early region 1B is insufficient for transformation, eliminating the possibility that region 1A is required only to induce such expression.

Identification of adenovirus 2 early region 4 polypeptides by in vitro translation and tryptic peptide map analysis

The mRNA species encoded by early region 4 (E4) (map position [mp] 91.5 to 99.3) of adenovirus 2 were isolated from the polysomes of infected KB cells and were purified by hybridization to the cloned HindIII-F fragment (mp 89.5 to 97.3) or to EcoRI-C fragment (mp 89.7 to 100). The mRNA's were translated in vitro using [35S]methionine as a labeled precursor in rabbit reticulocyte lysates treated with micrococcal nuclease as well as in wheat germ lysates. Five major (35,000-molecular-weight [35K], 23K, 22K, 21K, 18K) polypeptides were observed when the reticulocyte lysate was used. The 23K, 22K, 21K, and 18K polypeptides were also observed with the wheat germ lysate, as well as a very prominent 11K polypeptide; the 35K polypeptide was not observed. Assignment of these polypeptides to E4 was further established by hybrid arrested translation. Two-dimensional gel electrophoresis of a wheat germ translate resolved five polypeptides ranging from 18K to 23K, the major 11K polypeptide, and polypeptides of 10K and 9K. The in vitro 23K to 18K and 11K polypeptides migrated to approximately the same positions on two-dimensional gels as did seven 26K to 21K polypeptides and an 11K polypeptide synthesized in vivo (Brackmann et al., J. Biol. Chem, 255:6772--6779, 1980). Two-dimensional tryptic peptide maps demonstrated that the 35K, 23K, 22K, 21K, and 18K polypeptides are related. The peptide map of 11K is different from those of the above polypeptides, although 11K may share one tryptic methionine polypeptide with them. These results indicate that E4 encodes a major 11K polypeptide, as well as major 35K, 23K, 22K, 21K, and 18K polypeptides.

Nucleotide sequence of the transforming early region E1b of adenovirus type 12 DNA: structure and gene organization, and comparison with those of adenovirus type 5 DNA

The nucleotide sequence of the entire transforming early region of E1b of the highly oncogenic adenovirus type 12 (Ad12) DNA has been determined. The total sequence (3860 base pairs) encompasses the entire transforming early region E1 of Ad12 DNA. From the sequence for the E1b region of Ad12, and the transcription map of the E1b region (1, 2, 3, and this paper) the structure and gene organization of the early region E1b of Ad12 DNA were analyzed and compared with those of the E1b region in the non-oncogenic Ad5 DNA (4, 5). Most of the sequences in the E1b region of Ad12 was highly homologous to that of Ad5. It is predicted that the Ad12 region E1b codes for polypeptides of 53.9, 19.1, and 8.9 kd. This situation is identical with that of the Ad5 region E1b which codes for polypeptides of 54.9, 20.6, and 8.3 kd. The function of these predicted polypeptides encoded by the E1b regions in cell transformation is discussed.

Expression of early adenovirus genes requires a viral encoded acidic polypeptide

Host-range mutants of adenovirus 5 that contain a defect in region E1A (0-4.5 units) fail to replicate in HeLa cells and to transform rodent cells. In HeLa cells, these mutants synthesize only the two RNAs from E1A that share the same 5' and 3' termini but differ in length by the amount of internal sequence removed by splicing. RNA from wild-type virus, selected by hybridization to DNA from region E1A, translates into polypeptides of Mr 51,000 and 48,000 that are highly acidic in isoelectric focusing gels. These acidic Mr 51,000 and Mr 48,000 polypeptides are encoded by the longer and shorter E1A RNAs, respectively. Two of the host-range mutants, H5hr1 and H5hr2, fail to synthesize the Mr 51,000 polypeptide but do produce the Mr 48,000 polypeptide and a novel polypeptide thought to be a truncated portion of the Mr 51,000 polypeptide. H5hr1 and H5hr2 are hypothesized to have termination codons in sequences found only in RNA encoding the Mr 51,000 polypeptide. This prediction is verified for H5hr1 by DNA sequence analysis. The other three host-range mutants (H5hr3-5) synthesize both acidic polypeptides and are predicted to be missense. These results strongly imply that the Mr 51,000 polypeptide, alone or in combination with the Mr 48,000 polypeptide, is needed to regulate expression of adjacent viral genes during the early phase of adenovirus infection.

Coordinate regulation of two cytoplasmic RNA species transcribed from early region 2 of the adenovirus 2 genome

Early region 2 (E2) of the adenovirus 2 genome specifies a 72,000-dalton DNA-binding protein that is required for viral DNA replication. Electron microscopy studies have detected two major forms of 20S E2 mRNA, one species with a 5' leader from map position 75 and a second form having a leader from position 72 (Chow et al., J. Mol. Biol. 134:265-303, 1979). Only the species with a leader from position 75 was detected at early times; however, both forms were found at late times. We have analyzed the temporal regulation of E2 expression by documenting mRNA accumulation in the cytoplasm. Kinetic studies of pulse-labeled RNAs demonstrated a peak of E2 cytoplasmic RNa synthesis at 10 to 12 h, coinciding with the time of maximal synthesis of the 72,000-dalton DNA binding protein and viral DNA. To estimate the relative abundances of the two major E2 RNA species at various times during infection, total E2 cytoplasmic and polysomal 20S RNAs were isolated by hybridization-selection with specific DNA probes. The leader sequences in the selected RNAs were then quantitated by further RNA-DNA hybridization. We found that the elevated accumulation rate for E2 cytoplasmic RNA at late times reflected an increase in formation of both major species. Moreover, for all time points examined 66% of the mRNA species had a 5' end from map position 75, and 33% had a 5' terminus from position 72. Continuous labeling experiments provided evidence that both RNA forms have comparable half-lives. The results suggest that the two major species encoded by E2 are regulated in a coordinate fashion late in infection.

Protein kinase activity immunoprecipitated from adenovirus infected cells by sera from tumor-bearing hamsters

Earlier, we reported (N. J. Lassam, S. T. Bayley, F. L. Graham, and P. E. Branton, Nature (London) 277:241-243, 1979) detecting protein kinase activity when cytoplasmic extracts of human adenovirus type 5 (Ad5)-infected KB cells immunoprecipitated with 14b antitumor serum directed against the transforming proteins of Ad5, were incubated with [gamma-32P]ATP. Here we show that in the in vitro assay this kinase phosphorylated both the heavy chain of immunoglobulin G and polypeptide than comigrated on sodium dodecyl sulfate gels with the 58,000-dalton Ad5 antigen. It also phosphorylated added histone H3. Evidence is presented that the protein kinase activity found with extracts from Ad5-infected cells is not due to nonspecific trapping of cellular enzymes in immune complexes, but to an enzyme which is distinct from kinases detected at background levels in controls. Serine and threonine were the major phosphorylated amino acids, and essentially no phosphotyrosine was detected. Protein kinase activity detected in Ad12-infected cells immunoprecipitated by an antiserum derived from hamsters bearing Ad12-induced tumors appeared to be immunologically distinct from that immunoprecipitated from Ad5-infected cells by 14b serum.

Adenovirus early gene products may control viral mRNA accumulation and translation in vivo

The mechanisms controlling early adenovirus gene expression in vivo have been studied using inhibitors of protein synthesis. When inhibitors were added shortly before or at the onset of infection, viral mRNA from all early regions was transcribed, spliced and accumulated over a 7 hr period. After longer pretreatment, accumulation of several early mRNAs were suppressed. Addition of inhibitors 1 hr after infection enhanced the accumulation of viral mRNA in the cytoplasm. Translation of early mRNA selected on adenovirus DNA in a cell-free system reflected the amount of viral mRNA present. A viral coded product may therefore control accumulation of viral mRNA. A different pattern emerged when inhibitors of protein synthesis were removed at 5 hr postinfection and cells were removed at 5 hr postinfection and cells were pulse-labeled in vivo. If inhibitors were introduced at or before infection, early viral proteins were synthesized only after a lag of 1-3 hr. However, if treatment was introduced 1 hr postinfection, reversion of the protein synthesis block was instantaneous. It appears that protein synthesis inhibitors reveal an in vivo translational block for viral mRNA. This block could be overcome by preinfection with a related virus. Furthermore, no block was observed in a virus-transformed human embryonic kidney cell line (293) which expresses early region 1 of the viral genome. Viral gene product(s) encoded in early region 1 may control translation of early adenovirus messenger RNA in vivo.

Cloning of a DNA fragment from the left-hand terminus of the adenovirus type 2 genome and its use in site-directed mutagenesis

The HpaI E fragment (0-4.5 map units) of adenovirus type 2 (Ad2) DNA was cloned in the plasmid vector pBR322. Excision of the viral insert with PstI and XbaI generated a fragment which comigrated with Ad2 XbaI-E (0-3.8 map units), and this fragment was ligated to the 3.8-100 fragment generated by XbaI cleavage of the DNA of the Ad5 mutant, dl309 (N. Jones and T. Shenk, Cell 17:683-689, 1979). Transfection with the ligation products resulted in the production of progeny virus which was able to replicate on both HeLa and line 293 cells, demonstrating the biological activity of the sequences rescued from the plasmid. Small deletions were introduced around the SmaI site (map position 2.8) within the cloned viral insert, and the altered DNA sequences were reintroduced into progeny virus as described above. The mutant viruses grew well on line 293 cells but plaqued with greatly reduced efficiency on HeLa cells, exhibiting a host range phenotype similar to previously described mutants with lesions located within this region of the genome. When plasmid-derived left-end fragments containing pBR322 DNA sequences to the left of map position 0 were ligated to the 3.8-100 fragment of dl309 DNA, the infectivity of the ligation products was not reduced. However, all progeny viruses examined yielded normal-size restriction enzyme fragments from their left-hand ends, indicating that the bulk of the pBR322 DNA sequences are removed either prior to or as a consequence of the replication of the transfecting DNA molecules.

In vitro synthesis of adenovirus type 5 T antigens. I. Translation of early region 1-specific rna from lytically infected cells

Translation of early RNA specific for the leftmost early region 1 of adenovirus type 5 DNA in a rabbit reticulocyte cell-free system resulted in the synthesis of proteins with the following molecular weights: 65,000 (65K), 54K, 42 to 34K, 29K, 25K, 19K, and 18K. All of these proteins could be immunoprecipitated with hamster antitumor serum. The 42 to 34K proteins mapped in early region 1a, and those with molecular weights of 65K, 19K, and 18K mapped in early region 1b. The gene coding for the 54K protein may be localized outside of early region 1. We could not map unambiguously the 29K and 25K proteins. The identification of a 65K protein among products synthesized in vitro suggests that this protein may be identical to the 65K major T antigen present in adenovirus type 5-infected and -transformed cells, and this indicates that it is indeed encoded by the viral genome. This protein is encoded by a 23S mRNA. The other early region 1-specific proteins appear to be encoded by mRNA of approximately 13S, except for the 19K protein, which is synthesized with RNA sedimenting at both 13S and 23S.

Gene organization of the transforming region of weakly oncogenic adenovirus type 7: the E1a region

The structures of adenovirus type 7 (Ad7) cytoplasmic RNAs transcribed from the leftmost 4.5% of the viral genome during lytic infection of KB cells have been determined. The E1a region was found to specify three differently spliced mRNAs (I, II and III) which have common 5' and 3' termini. mRNAs I and II are transcribed between identical initiation and termination codons and code for polypeptides of 28 kd and 24 kd, whose only difference is an internal sequence of 32 amino acids present in the 28-kd protein. Translation of mRNA III initiates at the same AUG codon as in mRNA I and II, but uses a different reading frame beyond the splice point; consequently, it terminates at an earlier stop codon and yields a 6.3-kd polypeptide. Cytoplasmic E1a RNA was used as a template for in vitro protein synthesis in a cell-free system and found to encode polypeptides with apparent molecular weights of 42 kd, 40 kd, and 11 kd.

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.

The nucleotide sequence of the transforming early region E1 of adenovirus type 5 DNA

The sequence of the leftmost 11.3% of the non-oncogenic human adenovirus type 5 (Ad5) DNA has been determined. This segment contains the entire early region E1 of the Ad5 genome which has been shown to be involved in in vitro transformation of non-permissive rodent cells (Van der Eb et al., 1980). From the DNA sequence, and from the mRNA sequence data obtained by Perricaudet et al, (1979, 1980) for the E1 mRNAs from the closely related adenovirus type 2 (Ad2), it is possible to predict the primary structure of the polypeptides encoded by this region. The function of these proteins in cell transformation is discussed. From the positions of mapped restriction endonuclease sites and termini of RNA segments in the nucleotide sequence the length of the Ad5 DNA is estimated to be 36.6 kb.

New chimeric splice junction in adenovirus type 2-simian virus 40 hybrid viral mRNA

We have examined hybrid viral RNAs synthesized in both human and monkey cells infected by three nondefective adenovirus type 2 (Ad2)-simian virus 40 (SV40) hybrid viruses; Ad2+ND1, Ad2+ND2, and Ad2+ND4. Most of the hybrid viral RNA molecules appeared to be initiated within adenoviral sequences, but were polyadenylated on their 3' end at the early SV40 mRNA polyadenylation site. The Ad2+ND4 stock of virus was not homogeneous, but consisted of two principle populations of viral DNA. Both populations contained a segment of SV40 DNA extending from the SV40 map positions 0.63 to 0.11 in a left-to-right orientation at adenovirus map position 0.82. One population contained an intact SV40 segment, whereas the other (representing 80 to 85% of the population) has a 500-base pair deletion mapping from approximately 0.60 to 0.50 SV40 map units. This deletion encompassed the SV40 DNA segment which encodes the early SV40 splice sites. Cells infected by the mixed Ad2+ND4 population induced the synthesis of at least three major SV40 RNA species among the hybrid viral transcripts. The most abundant of these hybrid mRNA's appeared only late in the lytic cycle, after the onset of viral DNA replication. It contained an RNA splice junction which extended from a donor (5') nucleotide within the adenoviral RNA sequences to an acceptor (3') splice site within the early region of SV40 at 0.46 SV40 map units. This SV40 acceptor splice site was remarkable in that its use has not been detected in the spliced viral mRNA's of SV40-infected or -transformed cells.

Expression of unselected adenovirus genes in human cells co-transformed with the HSV-1 tk gene and adenovirus 2 DNA

We have introduced adenovirus 2 genes into high molecular weight DNA of permissive human cells by co-transformation of tk- human 143 cells with Ad2 restriction enzyme fragments and a cloned Bam HI fragment that carries the HSV-1 thymidine kinase gene. Tk+ cells were isolated after selection and maintenance in HAT medium. Several co-transformed lines are able to complement the growth of Ad5 dl312 (delta 1.2--3.7) and Ad5 dl434 (delta 2.6--8.7), deletion mutants that lack sequences from the left end of the viral genome. The amount and arrangement of viral sequences in the co-transformed cell lines have been analyzed by restriction endonuclease digestion and filter hybridization. Most of the cell lines contain a single insertion of the HSV-1 tk fragment and a single insert of adenoviral DNA. However, one line (B1) contains at least four different insertions, two of which are present in multiple copies. The adenoviral DNA in all cell lines is composed of sequences from the left end of the genome and extends for varying lengths in different lines. Two cell lines that complement deletion mutants efficiently synthesize both early region 1a and 1b mRNAs. The B1 line synthesizes low levels of 1a mRNA, higher levels of 1b mRNA and a unique mRNA that maps to the right of the 1b gene family. When grown continuously in HAT medium, some cell lines are quite stable while others are fairly unstable. Some tk+ subclones support the growth of viral mutants as well as the parental line while others give reduced levels of complementation. For all tk+ subclones examined, the alteration or reduction in viral gene expression is independent of changes in the pattern of integration of viral DNA.

Control of adenovirus early gene expression: a class of immediate early products

We have identified the viral mRNAs present in cells in which protein synthesis has been stringently inhibited prior to infection with adenovirus type 2. These species presumably represent the subset of viral mRNAs that are "immediate early" products, requiring only host cell genes of their expression, and they do not include any of the conventionally recognized early mRNAs. Treatment of cells with 100 microM anisomycin inhibits 99.6% of protein synthesis and substantially depresses (by 20--200 fold) the levels of the conventional early mRNAs from regions E1A, E1B, E2, E3 and E4. Also depressed are species encoding an 87K protein (11.6--31.5 map units) and a 13.6K protein (encoded a short distance to the right of 21.5 map units). The only mRNAs not depressed by this treatment are an mRNA for a 13.5K protein encoded between 17.0 and 21.5 map units, and the mRNA for the late 52,55K protein encoded between 29 and 34 map units, which is also present in small amounts at early times. Further proof that production of the mRNA for the immediate early 13.5K protein is independent of E1A gene function is provided by the observation that it can be detected in cells infected with the E1A deletion mutant dl312.

Predicted structure of two adenovirus tumor antigens

Early adenovirus type 2(Ad2) mRNA sequences have been cloned by using the pBR322 plasmid as a vector. Two clones that include sequences from region E1B were identified and their DNAs were characterized by hybridization, restriction enzyme cleavage, and DNA sequence analysis. The results showed that the clones were derived from two different spliced mRNAs. By combining our results with the established DNA sequence for region E1B of the closely related adenovirus type 5[Maat, J., van Beveren, C.P. & van Ormondt, H. (1980) Gene, in press] it was possible to deduce the structure of a 13S and a 22S mRNA. The two mRNAs differ from each other by the size of their intervening sequences. If translation starts at the first AUG following the cap, the 22S mRNA encodes a Mr 67,000 polypeptide that is terminated by a UGA stop codon located immediately before the splice, whereas the 13S mRNA encodes a Mr 20,000 polypeptide that is translated in different reading frames before and after the splice. The Mr 20,000 and 67,000 polypeptides correspond in molecular weight to two proteins that invariably are precipitated from infected cell extracts by antisera from animals carrying adenovirus-induced tumors.

Adenovirus type 2 terminal protein: purification and comparison of tryptic peptides with known adenovirus-coded proteins

The protein covalently bound to the 5' termini of adenovirus type 2 DNA has been purified from virus labeled with [35S]methionine, using exclusion chromatography of disrupted virions to isolate the DNA-protein complex, which is then digested with DNase. The terminal protein isolated from mature virus is most effectively labeled if the cells are exposed to [35S]methionine during the "intermediate" period of 13 to 21 h postinfection, suggesting that the protein is synthesized during this interval. The tryptic peptides of the terminal protein were compared with those of several known adenovirus-coded proteins and found to be unrelated. In particular, the terminal protein is not related to the 38-50K early proteins encoded by the leftmost 4.4% of the adenovirus genome, one region essential for the transforming activity of the virus. Neither is it related to the 72K single-strand-specific DNA binding protein, the minor virion component IVa2, or the major capsid component hexon.