Characterization of adenovirus type 2 transcriptional complexes isolated from infected HeLa cell nuclei

Morphological, Biochemical, and Functional Study of Viral Replication Compartments Isolated from Adenovirus-Infected Cells

Adenovirus (Ad) replication compartments (RC) are nuclear microenvironments where the viral genome is replicated and a coordinated program of late gene expression is established. These virus-induced nuclear sites seem to behave as central hubs for the regulation of virus-host cell interactions, since proteins that promote efficient viral replication as well as factors that participate in the antiviral response are coopted and concentrated there. To gain further insight into the activities of viral RC, here we report, for the first time, the morphology, composition, and activities of RC isolated from Ad-infected cells. Morphological analyses of isolated RC particles by superresolution microscopy showed that they were indistinguishable from RC within infected cells and that they displayed a dynamic compartmentalization. Furthermore, the RC-containing fractions (RCf) proved to be functional, as they directed de novo synthesis of viral DNA and RNA as well as RNA splicing, activities that are associated with RC in vivo. A detailed analysis of the production of viral late mRNA from RCf at different times postinfection revealed that viral mRNA splicing occurs in RC and that the synthesis, posttranscriptional processing, and release from RC to the nucleoplasm of individual viral late transcripts are spatiotemporally separate events. The results presented here demonstrate that RCf are a powerful system for detailed study into RC structure, composition, and activities and, as a result, the determination of the molecular mechanisms that induce the formation of these viral sites of adenoviruses and other nuclear-replicating viruses.

IMPORTANCE

RC may represent molecular hubs where many aspects of virus-host cell interaction are controlled. Here, we show by superresolution microscopy that RCf have morphologies similar to those of RC within Ad-infected cells and that they appear to be compartmentalized, as nucleolin and DBP display different localization in the periphery of these viral sites. RCf proved to be functional, as they direct de novo synthesis of viral DNA and mRNA, allowing the detailed study of the regulation of viral genome replication and expression. Furthermore, we show that the synthesis and splicing of individual viral late mRNA occurs in RC and that they are subject to different temporal patterns of regulation, from their synthesis to their splicing and release from RC to the nucleoplasm. Hence, RCf represent a novel system to study molecular mechanisms that are orchestrated in viral RC to take control of the infected cell and promote an efficient viral replication cycle.

RNA elongation by RNA polymerase II is not inhibited by N-ethylmaleimide or iodoacetamide

The elongation of RNA by RNA polymerase II is not inhibited by N-ethylmaleimide or iodoacetamide. Three systems were studied: a soluble chromatin, purified RNA polymerase II with DNA, and a HeLa cell extract with an adenovirus 2 promoter sequence.

Linear adenovirus DNA is organized into supercoiled domains in virus particles

Electron microscopic analysis of bis-psoralen crosslinked adenovirus type 5 virion DNA revealed supercoiled domains in an otherwise linear DNA. The existence of supercoiled arrangement in all the virion DNA was demonstrated by the sensitivity of Ad5 DNA in pentonless virus particles to the supercoiling-dependent endonucleolytic activity of Bal31 and S1 nucleases. These nucleases were found to cleave Ad5 virion DNA at specific sites. The observation of stable cleavage sites in the limit digestion of virion DNA by Bal31 suggests that cleavage sites represent boundaries of core proteins which impede the exonuclease activity of Bal31. These data suggest that specific arrangement of core proteins on Ad5 virion DNA. Based on this analysis we determined positions of core proteins in viral genome using indirect end labeling technique. The size of supercoiled domains of virion DNA was estimated by electron microscopy and also by boundaries of mutually exclusive Bal31 cleavage sites at limit digestion condition. Our data suggest each supercoiled domain is equal to about 12% of Ad5 genome length and about 8 loops can be accommodated in Ad5 virion. However sequences at two extreme ends of the viral genome were found to be outside of supercoiled domains. An interesting correlation between supercoiled domains and gene domains of Ad5 genome was noticed.

Adenovirus transcriptional complexes contain EIa encoded tumour antigens physically bound to cellular proteins

Adenovirus type 12 transcriptional complexes were isolated from cells during the early phase of infection. Sedimentation analysis identified a fast sedimenting complex type I and a slow sedimenting complex type II. Both complexes made virus specific RNA complementary to all the early genes and both contained viral DNA, which in type II but not in type I had nucleosome like configuration. Analysis of the proteins of the complexes with antiserum against Ad 12 EIa-beta-galactosidase fusion protein expressed in E. coli demonstrated the following: (a) type I complex contained EIa 45 K protein, which co-precipitated with cellular proteins of mol. wt. 42, 58, and 60 K, (b) type II complex contained EIa 47 K protein, which co-precipitated with major cellular proteins of 35, 40-46 K and minor proteins of 58, 60, 68, 76, 86, and 120-150 K. Association of EIa specific and cellular proteins to transcriptional complexes was sensitive to both 1 M NaCl and DNAse I indicating the DNA binding nature of these proteins. Treatment of transcriptional complexes with 1 M NaCl or DNase I released EIa proteins, which still remained strongly bound to cellular proteins. These findings suggested that EIa proteins bind to viral DNA and that this binding is probably mediated by cellular proteins.

The abundance and in vitro DNA binding of three cellular proteins interacting with the adenovirus EIIa early promoter are not modified by the EIa gene products

Specific protein binding on the EIa-inducible adenovirus EIIa early (EIIaE) promoter was analyzed by the sensitive electrophoretic band-shift assay and by protection against DNase I digestion. Three factors were identified, and precise mapping of the cognate-binding sites revealed their correspondence to promoter elements essential for constitutive EIIaE transcription. One binds to the major upstream element located between -82 and -64 (with respect to the major EIIaE cap site), another appears to interact with sequences on either side of this region, and the last one binds to an element located further upstream. Comparison of the binding activities of the factors present in extracts from cells infected with wild-type adenovirus (adenovirus type 5) or with the EIa deletion mutant dl312 did not reveal striking differences. Not only were the general binding patterns indistinguishable, but the concentration of each of the identified factors as well as their affinity for the cognate-binding sites were unchanged. Our results suggest that the EIa-mediated activation of the EIIaE transcription complexes involves appropriate interactions between transcription factors, rather than their increased binding to DNA.

The abundance and in vitro DNA binding of three cellular proteins interacting with the adenovirus EIIa early promoter are not modified by the EIa gene products

Specific protein binding on the EIa-inducible adenovirus EIIa early (EIIaE) promoter was analyzed by the sensitive electrophoretic band-shift assay and by protection against DNase I digestion. Three factors were identified, and precise mapping of the cognate-binding sites revealed their correspondence to promoter elements essential for constitutive EIIaE transcription. One binds to the major upstream element located between -82 and -64 (with respect to the major EIIaE cap site), another appears to interact with sequences on either side of this region, and the last one binds to an element located further upstream. Comparison of the binding activities of the factors present in extracts from cells infected with wild-type adenovirus (adenovirus type 5) or with the EIa deletion mutant dl312 did not reveal striking differences. Not only were the general binding patterns indistinguishable, but the concentration of each of the identified factors as well as their affinity for the cognate-binding sites were unchanged. Our results suggest that the EIa-mediated activation of the EIIaE transcription complexes involves appropriate interactions between transcription factors, rather than their increased binding to DNA.

A general transcription factor forms a stable complex with RNA polymerase B (II)

A general transcription factor (BTF3) has been purified from HeLa whole cell extracts and shown to be required for accurate initiation of transcription from the adenovirus-2 major late promoter (Ad2MLP) and other RNA polymerase class B promoters. We show that purified BTF3 (27 kd) binds to RNA polymerase B (II), forming a complex that is transcriptionally active. We found no evidence that purified BTF3 interacts with DNA or is required for the formation of the stable preinitiation complex.

Adenovirus E1a proteins repress transcription from the SV40 early promoter

Using a transient expression assay in HeLa cells, we show that products from the adenovirus-5 E1a transcription unit repress transcription from the SV40 early promoter. The repression is unrelated to T antigen autoregulation, occurs maximally with low concentrations of E1a expression plasmid, is exerted at the transcriptional level, and requires functional E1a protein. The 289 and 243 amino acid E1a proteins are equally effective at repressing transcription. Since only the 289 amino acid protein is efficient at activating transcription, we conclude that activation and repression are separate E1a functions. We discuss possible mechanisms for E1a repression and the relationship of repression to the function of E1a in cell immortalization and transformation.

Glucocorticoid regulation of transcription at an amplified, episomal promoter

The mouse mammary tumor virus long terminal repeat (MMTV LTR) has been introduced into cultured murine cells, using the 69% transforming fragment of bovine papilloma virus type 1 (BPV). Transformed cells contain up to 200 copies of the chimeric molecules per diploid genome. The restriction endonuclease map of the acquired recombinants, as well as the physical structure of the DNA, indicates that the LTR-BPV molecules present in these cells occur exclusively as unintegrated, extrachromosomal episome. When a 72-base pair direct repeat "enhancer" element (derived from the Harvey sarcoma retrovirus) was included in the MMTV LTR-BPV chimeric plasmids, DNA acquired through transfection, with a single exception, was integrated or rearranged or both. The transcriptional potential of the episomal MMTV promoter present in these cells was tested in two ways. First, steady-state levels of MMTV-initiated RNA were measured by quantitative S1 mapping. Second, the relative number of transcription complexes initiated in vivo was determined by using a subnuclear fraction highly enriched for MMTV-BPV minichromosomes in an in vitro transcription extension assay. Both approaches showed that the MMTV LTR present in the episomal state was capable of supporting glucocorticoid hormone-regulated transcription. We have therefore demonstrated the hormone response for the first time in a totally defined primary sequence environment. Significant differences both in the basal level of MMTV-initiated transcription and in the extent of glucocorticoid induction were observed in individual cell lines with similar episomal copy numbers. These phenotypic variations suggest that epigenetic structure is an important component of the mechanism of regulation.

Glucocorticoid regulation of transcription at an amplified, episomal promoter

The mouse mammary tumor virus long terminal repeat (MMTV LTR) has been introduced into cultured murine cells, using the 69% transforming fragment of bovine papilloma virus type 1 (BPV). Transformed cells contain up to 200 copies of the chimeric molecules per diploid genome. The restriction endonuclease map of the acquired recombinants, as well as the physical structure of the DNA, indicates that the LTR-BPV molecules present in these cells occur exclusively as unintegrated, extrachromosomal episome. When a 72-base pair direct repeat "enhancer" element (derived from the Harvey sarcoma retrovirus) was included in the MMTV LTR-BPV chimeric plasmids, DNA acquired through transfection, with a single exception, was integrated or rearranged or both. The transcriptional potential of the episomal MMTV promoter present in these cells was tested in two ways. First, steady-state levels of MMTV-initiated RNA were measured by quantitative S1 mapping. Second, the relative number of transcription complexes initiated in vivo was determined by using a subnuclear fraction highly enriched for MMTV-BPV minichromosomes in an in vitro transcription extension assay. Both approaches showed that the MMTV LTR present in the episomal state was capable of supporting glucocorticoid hormone-regulated transcription. We have therefore demonstrated the hormone response for the first time in a totally defined primary sequence environment. Significant differences both in the basal level of MMTV-initiated transcription and in the extent of glucocorticoid induction were observed in individual cell lines with similar episomal copy numbers. These phenotypic variations suggest that epigenetic structure is an important component of the mechanism of regulation.

Adenovirus type 2 DNA replicated in arginine-starved KB cells is infectious

Adenovirus type 2 DNA from extracts of KB cells rendered nonpermissive by arginine starvation is infectious.

Specific in vitro initiation of transcription on the adenovirus type 2 early and late EII transcription units

Three transcription units are present in the adenovirus type 2 region EII. Transcription units EIIaE and EIIaL encode the mRNA for the 72,000-dalton DNA binding protein, early and late in the lytic cycle, respectively, and transcription unit EIIb encodes the mRNA for the protein that binds to the 5' termini of adenovirus DNA. By using a cell-free transcription system in the presence of purified RNA polymerase B (or II), we have obtained specific initiation of transcription from both the EIIaE promoter, which does not contain a T-A-T-A box, and the EIIaL promoter, which does. In addition, we have identified a new EII T-A-T-A box promoter that is located close to the early non-T-A-T-A box promoter and is used both in vivo and in vitro.

Protein kinases associated with the adenovirus single-stranded DNA-binding protein

Protein kinase activities copurifying with the 72000-Mr DNA-binding protein of adenovirus on DNA-cellulose chromatography and gel filtration in acrylamide/agarose have been partially characterized and purified. One of these kinases was found to phosphorylate efficiently the viral DNA-binding protein in vitro and to be stimulated severalfold by the addition of histones, protamine, or polyamines. The kinase does not, however, phosphorylate histones, protamine, casein, or phosvitin. A second protein kinase was also recovered from single-stranded DNA-cellulose which is able to phosphorylate the 72000-Mr DNA-binding protein, but which is inhibited by the addition of histones. Phosphorylation in vitro of the 72000-Mr DNA-binding protein from the ts125 mutants of adenovirus by the histone-stimulated protein kinase was found to be thermosensitive.

Nuclear ribonucleoprotein particles from adenovirus infected Hela cells

Heterogenous nuclear RNA-protein complexes (hnRNP) from adenovirus-2 (Ad-2) infected Hela cells contain most of the virus-specific RNA which is labeled in the nucleus during periods lasting from 45 seconds to 2 hours. Moreover, the percentage of RNA which is Ad-2 specific as monitored by filter hybridization increases progressively from early to late period where it accounts for as much as 50-60% of the labeled RNA. The Ad-2 sequences are found in heterogenous complexes sedimenting between 30 and 200 S the density of which in CsCl (rho approximately 1.39) as well as metrizamide (rho approximately 1.29) seems to be the same as that of the bulk particles. A more detailed analysis with restriction fragments shows that all regions of the Ad-2 genome are represented in these particles.

Analysis of herpes simplex virus nucleoprotein complexes extracted from infected cells

HEp-2 cells were infected with herpes simplex virus type 1 and labeled with [3H]thymidine and 14C-amino acids. Infected cells or nuclei prepared from them were extracted with Triton X-100 and NaCl, utilizing a method recently described, and the low-speed supernatant (extract) was partially purified by sedimentation on sucrose gradients. A nucleoprotein complex which sedimented as a wide peak around 200S was identified. The nucleoprotein complex contained viral DNA, which banded at the expected density in CsCl isopycnic gradients and was intact after measurements taken on electron microscopic photographic enlargements. The autoradiographic pattern of 14C-labeled proteins after electrophoresis showed that only a few of the virus-specific polypeptides were present in the nucleoprotein complexes, in particular, VP5, VP12, VP15.2, VP19, and VP24. Cellular histones were absent. The extracts and the nucleoprotein complexes were centrifuged to equilibrium in metrizamide density gradients without prefixation. Electron microscopic direct visualization of the nucleoprotein complexes after sucrose or metrizamide purification revealed that the proteins were preferentially associated with one end of the DNA molecule and formed large irregular terminal thickenings or capsid-like transparent shells enclosing polyglobular cores. No nucleosomes were observed on herpes simplex virus nucleoprotein complexes. The same type of complex was detected after phosphonoacetic acid addition, and grossly altered nucleocapsids were formed.

Visualization of genetic recombination intermediates of human adenovirus type 2 DNA from infected HeLa cells

The study of recombination in prokaryotes has been facilitated by the availability of recombinational mutants and simple genetic elements such as phages and plasmids. These small but defined molecules of DNA have been especially useful for electron microscopic analysis of structural detail of molecules undergoing recombination both in vivo and in vitro. A limitation in the structural analysis of plasmid recombination is the absolute number of recombining molecules which can be identified and analysed amidst a background of nonrecombining molecules. This limitation would be of even greater consequence in studies of genetic recombination in animal cells. We therefore chose virus-infected animal cells as a model system for the study of the molecular mechanism of genetic recombination in higher organisms. HeLa cells infected with adenovirus serotype 2 (Ad-2) offer several advantages for studying recombination: (1) the virus contains a small and well characterized genome of about 35 kilobases; (2) a large amount of Ad-2 DNA is accumulated during lytic infection and host DNA synthesis is suppressed; (3) Ad-2 recombines at a very high frequency; and (4) similar to phages, animal viruses and Ad-2 in particular are believed to use many of the host cell's enzymes in necessary metabolic processes, presumably including recombination. In this study we used electron microscopic techniques to visualize the structures of in vivo Ad-2 DNA recombination intermediates. Molecules were observed with structures at putative cross-over points which were consistent with the molecular mechanism of recombination proposed by Holliday. In addition, we observed Ad-2 DNA molecules engaged in recombination which were simultaneously serving as templates for replication and/or transcription. To the best of our knowledge, this is the first visualization of in vivo recombination intermediates of discrete DNA molecules isolated from eukaryotic cells.

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.

Characterization of simian virus 40 transcriptional intermediates in infected CV1 cell nuclei

Simian Virus (SV40) transcriptional intermediates (T.I.) were isolated from infected cell nuclei incubated in vitro in the presence of the four ribonucleoside triphosphates. The nascent mRNA strands in the viral DNA-RNA hybrid molecules were hydrogen bonded to their template by 200-250 nucleotides on the average, as judged from the extent of their RNase resistance and the aspect of T.I. under electron microscope after treatment with 50 per cent formamide. The RNA polymerase involved (RNA polymerase II) synthesized up to full length transcripts at a rate of approximately 150 nucleotides/min. at 25 degrees C. Each SV40 infected cell was found to contain about 200 active T.I. molecules at the peak of late transcription. The DNA in the T.I. molecules was exclusively form I DNA only in cell infected with the tsA30 mutant of SV40 that had been transferred to non-permissive temperature in order to arrest DNA replication, but both form I DNA and molecules behaving as replicative intermediates (R.I.) in wild type infected cells.

Adenovirus DNA template for late transcription is not a replicative intermediate

The relationship between adenovirus replication and late transcription has been investigated using viral replication and transcription complexes isolated from infected HeLa cell nuclei. These two types of complexes extracted from adenovirus type 2-infected cell nuclei did not sediment at the same rate on sucrose gradients. Viral replicative intermediates were quantitatively precipitated by immunoglobulins raised against purified 72,000-dalton DNA-binding protein, whereas viral transcription complexes remained in the supernatant. These results show that late transcription does not occur on active replication complexes or on 72,000-dalton DNA-binding protein-containing replicative intermediates inactive in DNA synthesis. Additional evidence is presented indicating that it is very unlikely that replicative intermediates lacking the 72,000-dalton DNA-binding protein could be the template for late transcription.

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.

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.

Effect of histone acetylation on structure and in vitro transcription of chromatin

n-Butyrate treatment of growing Hela cells produces a dramatic increase in the levels of histone acetylation. We have exploited this system to study the effect of histone acetylation on chromatin structure. Chromatin containing highly acetylated histones is more rapidly digested to acid-soluble material by DNase I, but not by micrococcal nuclease. The same pattern of nuclease sensitivity was exhibited by in vitro-assembled chromatin consisting of SV40 DNA Form I and the 2 M salt-extracted core histones from butyrate-treated cells. Using this very defined system, it was possible to demonstrate that acetylated nucleosomes do not have a greatly diminished stability. Stability was measured in terms of exhange of histone cores onto competing naked DNA or sliding of histone cores along ligated naked DNA. Finally, it was shown that acetylated nucleosomes are efficient inhibitors of in vitro RNA synthesis by the E. coli holoenzyme as well as by the mammalian polymerases A and B.

Enzymatic properties of viral replication complexes isolated from adenovirus type 2-infected HeLa cell nuclei

When HeLa cell nuclei, isolated 17 h after infection with adenovirus type 2 (Ad2), were extracted with 200 mM ammonium sulfate, Ad2 nucleoprotein complexes were selectively released. These complexes contained a DNA polymerase activity that corresponded to DNA polymerase molecules actively engaged in Ad2 DNA replication. Under our high-salt (200 mM ammonium sulfate) incubation conditions, where no reinitiation occurred, full-length Ad2 DNA chains were synthesized by elongation of chains that had been initiated in vivo. This conclusion was further supported by density labeling experiments indicating that the in vitro DNA synthesis was semiconservative. Evidence is presented suggesting that at least part of the DNA polymerase molecules engaged in Ad2 DNA replication belong to the gamma class.

Replication of adenovirus type 2 DNA in vitro

A soluble replication system that synthesizes full-sized adenovirus DNA molecules has been developed. The extraction of infected HeLa nuclei solubilizes approximately 25% of the viral replicating DNA and leaves the HeLa chromatin associated with the insoluble nuclear material. Both the extracted viral DNA and the DNA product synthesized in vitro are intact and identical to the adenovirus DNA or its replicating intermediates produced in whole infected cells. The direction of elongation and the termini of replication of progeny DNA in vitro are essentially identical to those observed in vivo. Nuclear extract replication is dependent on Mg2+ and the four deoxyribonucleoside triphosphates and partially stimulated by ATP.