Transcriptional control signals in the genome of bovine papillomavirus type 1

Cellular factors are required to activate bovine papillomavirus-1 early gene transcription and to establish viral plasmid persistence but are not required for cellular transformation

Transcription from the major upstream early gene promoter, P89, of bovine papillomavirus (BPV)-1 is detectable in transfected cells lacking viral gene products yet also responds to viral E2 proteins. In contrast to human papillomaviruses (HPVs), the BPV upstream regulatory region (URR) functions as a transcriptional enhancer in epithelial cells and fibroblasts of bovine, murine or human origin. Mutations of Sp1 and/or two novel transcriptional enhancer factor (TEF)-1 sites within the 5' URR of the intact BPV-1 genome dramatically reduced P89-initiated mRNA levels, leading to decreased BPV-1 plasmid amplification and inefficient formation of transformed cell foci. However, cell lines transformed with wt or mutant BPV-1 genomes contained similar levels of unintegrated BPV-1 DNA, P89 mRNA and E2-dependent transactivation. We conclude that cellular factors necessary for activating viral early gene transcription, establishment of viral plasmid replication and cell immortalization are not required during the maintenance phase of BPV-1 infection.

Organization and expression of the genome of bovine papillomavirus type 1

The viral mRNAs present in C127 cells transformed by bovine papillomavirus type 1 (BPV-1) have been mapped by a variety of techniques, including S1 nuclease analysis, Northern blot analysis, primer extension and electron microscopic heteroduplex analysis. The results reveal a very complex mRNA pattern, comprising at least five types of spliced cytoplasmic mRNAs. Both unspliced and partially processed nuclear RNA species have also been identified. The transforming region of BPV-1 contains several promoter regions. A major cap site is located at coordinate 1 and another putative cap site at coordinate 31. A third candidate cap site maps around coordinate 39.

Derivation and partial analysis of two highly active myeloma cell transfectants

Vectors have been designed to optimise the expression of heterologous proteins in transfected mouse myeloma cells. The over-ridingly important DNA element contained in these constructs is the classical mouse immunoglobulin heavy chain enhancer. It is shown that even in the absence of a well-known promoter element, the enhancer can drive gene expression in stable cell transfectants and the main transcriptional start site utilized in such situations has been mapped to within the previously defined enhancer region. Using chicken lysozyme as a reporter function in these vectors, two transfected myeloma cell clones have been isolated which secrete this protein at levels 50-100-times as high as those usually obtained with the same vectors and it is shown that in molar terms this is at least as high as endogenous immunoglobulin produced by a related line. Analysis of these lines show that in one case only a single copy, and in the other two to three copies, of the apparently unrearranged vector have integrated at a single locus within the genome. Possible explanations for the high-level expression are discussed.

The bovine papillomavirus constitutive enhancer is essential for viral transformation, DNA replication, and the maintenance of latency

Bovine papillomavirus type 1 (BPV-1) has served as the prototype papillomavirus for the study of viral transcription, DNA replication, and latency. However, no cis essential transcription control regions which are necessary for both transformation and replication of BPV-1 or any other papillomavirus have yet been defined. We have found that BPV-1 mutants with deletions in the long control region were defective for transformation and replication, with the essential region in the 5' long control region corresponding to the previously defined BPV-1 constitutive enhancer (S. B. Vande Pol and P. M. Howley, J. Virol. 64:5420-5429, 1990). BPV-1 mutants deleted of the constitutive enhancer could be complemented in trans by the full-length virally encoded E2 transactivator and replication factor (E2TA) and in cis by the simian virus 40 enhancer. The constitutive enhancer induced the production of E2TA by activating all the major viral early promoters upstream of the E2 open reading frame. Complementation experiments using a temperature-sensitive E2TA mutant indicated that the constitutive enhancer was necessary for the maintenance of viral DNA replication within latently infected cells and implied that viral transcription under the regulation of the constitutive enhancer may be controlled during the cell cycle. The constitutive enhancer is a master regulatory control region for establishing and maintaining BPV-1 latency, and its characteristics reveal some analogies with cell type-specific enhancer elements recognized in the human papillomaviruses.

A bovine papillomavirus constitutive enhancer is negatively regulated by the E2 repressor through competitive binding for a cellular factor

The bovine papillomavirus type 1 long control region (LCR) contains DNA sequence elements involved in the regulation of viral transcription and replication. Differences in the levels of transcription have previously been noted between bovine papillomavirus type 1-infected rodent cell lines and bovine cells. To investigate these differences, fragments of the LCR were cloned into an enhancer-deleted chloramphenicol acetyltransferase expression vector and assayed for enhancer activity. A strong constitutive enhancer was found in the 5' portion of the LCR that was most active in primary bovine fibroblasts and had little activity in other cell types. Deletion mapping localized most of the activity to a 113-bp fragment from nucleotides (nt) 7162 to 7275, a region of the viral sequence that also contains the P7185 promoter and an E2-binding site at nt 7203. The enhancer activity of this element could be positively modulated by the full-length E2 transactivator or negatively modulated by the E2 repressor. Site-directed mutagenesis defined two cis elements, CE1 and CE2, which were both necessary for enhancer activity. The CE1 element was required for P7185 activity, whereas the CE2 element was dispensable for P7185 activity. The CE1 and CE2 elements both overlap the E2-binding site at nt 7203. In vitro DNA-binding studies revealed (i) a specific gel retardation complex associated with cellular factor binding at the CE1 element, (ii) a correlation between enhancer activity and the binding of factors to the CE1 element, and (iii) competitive binding between the E2 repressor and the cellular factor at the CE1 element.

A novel spontaneous mutation of the bovine papillomavirus-1 genome

A cell clone (cl.2) having an atypical transformed morphology was isolated from a murine C127 cell culture experimentally infected with a bovine papillomavirus type 1 (BPV-1) virion preparation. cl.2 cells exhibited minimal transformed characteristics and contained multiple copies of a BPV-1 plasmid with a molecular size slightly less than that of the wild type viral genome. A simple deletion of 277 bp was mapped to the distal portion of the viral 69% transforming fragment where the early gene region merges with the late gene region. None of the recognized early open reading frames were affected by the deletion but sequences including the common early gene mRNA polyadenylation (poly(A] signal and several base pairs of the "distal" enhancer element were deleted. Transfection of C127 cultures with low molecular weight (Hirt) DNA prepared from cl.2 cells led to the appearance of transformed cell foci, and Southern blotting analysis of a cl.2 Hirt DNA-transformed cell line confirmed that the deletion did not destroy the ability to replicate as a high copy plasmid. Removal of the natural early poly(A) signal did not obligate use of the alternative natural viral poly(A) signal located towards the end of the late region. Instead, a new major early mRNA polyadenylation site was mapped close to the unique BamHI recognition sequence at the distal end of the transforming region. Our results underline previous observations that there is a block to the production of stable mRNAs from the late gene region in BPV-1-transformed C127 cells, yet this is not necessarily explained by premature termination of transcription within this region.

cis activation of the c-myc gene in bovine papilloma virus type 1/human c-myc hybrid plasmids

The c-myc gene amplification observed in human tumors is likely to represent an activation mechanism aiming at an increased transcription level. In order to evaluate the biological significance of this amplification in the malignant transformation we have designed an experimental model that could possibly mimic this situation in vitro. We have constructed a series of plasmids which physically link the human c-myc gene to the bovine papilloma virus type 1 genome (BPV1) and therefore should be maintained as amplified episomes upon transformation of rodent cells. Anticipating that the high copy number will bring about the immortalizing capacity of the c-myc gene, the constructions were introduced into primary rat embryo cells. Immortal cell lines were established by transfection of the hybrid plasmids carrying either the complete BPV1 genome or the transforming region of the viral genome. The BPV1 DNA alone or the c-myc gene alone has no activity in this assay. The analysis of the established cell lines demonstrates that the transfected plasmids are present not as free copies as anticipated but rather integrated as tandem repeats. We present data which strongly suggest that the immortalization capacity of the hybrid plasmids reflects the activation of the c-myc gene by the transactivable BPV1 enhancer. Although both the BPV1 early genes and the c-myc gene are actively transcribed, most of the cell lines do not display a transformed phenotype.

Messenger RNAs from the E1 region of bovine papillomavirus type 1 detected in virus-infected bovine cells

Bovine papillomavirus type 1 DNA replicated to a high copy number in virus-infected bovine fibroblasts. Infected bovine cells were therefore used as a source of RNA for Northern blotting analysis to search for viral transcripts hybridizing to the E1 gene region, implicated in viral DNA replication. Cytoplasmic polyadenylated RNA preparations contained at least five different E1-region transcripts, ranging from 1200 to approximately 4500 nucleotides in length. All of these species contained sequence information from the 5'-end of the E1 open reading frame, but only the largest species included sequences from its central portion. The latter transcript is a candidate mRNA for a stimulatory replication factor (R) previously mapped by genetic experiments (1).

Bovine papillomavirus type 1 3' early region transformation and plasmid maintenance functions

We examined bovine papillomavirus type 1 (BPV-1) DNAs mutated in the E2 open reading frame (ORF) to determine their ability (i) to transform C127 cells and (ii) to remain extrachromosomal in transfected cells. Results obtained with deletion mutants and insertion mutants containing a linker with translational termination codons in all possible reading frames indicated that an E2 ORF gene product(s) is necessary for efficient transformation, as well as viral plasmid replication and maintenance in the context of the full BPV-1 genome. Complementation assays in which mutant BPV-1 DNAs were transfected into cell lines expressing some viral functions from integrated BPV-1 cDNAs demonstrated that the E2 ORF product, when provided in trans, could allow BPV-1 E2 mutants to remain extrachromosomal. The E2 function could also augment transformation of some, but not all, BPV-1 E2 mutants, allowing identification of another region of BPV-1 involved in cellular transformation. It is likely that the role of the BPV-1 E2 product(s) in transformation and plasmid maintenance is indirect. A BPV-1 mutant altered in the E5 ORF is transformation defective and unable to replicate as a stable plasmid in C127 cells.

The bovine papillomavirus distal "enhancer" is not cis essential for transformation or for plasmid maintenance

We constructed a mutant of bovine papillomavirus type 1 (BPV-1) DNA that lacked a transcriptional enhancer located 3' to the polyadenylation site of the early viral RNAs expressed in transformed cells. This mutant DNA, when separated from the procaryotic sequences, transforms mouse cells with an efficiency comparable to that of the full BPV-1 genome, and it exists as a stable multicopy plasmid in transformed cells. The BPV-1 distal enhancer suppresses the effects of a cis-inhibitory element in pML2 sequences but is not essential for the expression of the viral genes involved in cellular transformation or plasmid maintenance.

Properties of intracellular bovine papillomavirus chromatin

Episomal nucleoprotein complexes of bovine papillomavirus type 1 (BPV-1) in transformed cells were exposed to DNase I treatment to localize hypersensitive regions. Such regions, which are indicative for gene expression, were found within the noncoding part of the genome, coinciding with the origin of replication and the 5' ends of most of the early mRNAs. However, there were also regions of hypersensitivity within the structural genes. These intragenic perturbations of the chromatin structure coincide with regulatory sequences at the DNA level. One of these regions maps in close proximity to a Z-DNA antibody-binding site which is located near the putative BPV-1 enhancer sequence.

Nuclear activity from F9 embryonal carcinoma cells binding specifically to the enhancers of wild-type polyoma virus and PyEC mutant DNAs

Although wild-type polyoma virus does not productively infect murine embryonal carcinoma (EC) cells, a number of mutants (PyEC mutants) that do infect undifferentiated EC cells have been isolated. All PyEC mutants have DNA sequence alterations within the enhancer region of the viral genome. This report describes an activity present in nuclear extracts of F9 EC cells which, by "footprint" analyses, binds specifically to a small region of about 20 base pairs (nucleotides 5180-5200) within the subregion of the polyoma enhancer designated as the B or beta element. While no difference in binding of factor was detected between wild-type polyoma enhancer and the enhancers of the PyEC mutants, PyF111 and PyF441, which had been selected for productive infection of F9 cells, definite differences between wild-type and mutants were observed in the digestion patterns of their naked DNAs with either DNAase I or exonuclease III. This difference was restricted to the region around the point mutation (nucleotide 5258) common to these mutant DNAs.

E5 open reading frame of bovine papillomavirus type 1 encodes a transforming gene

We have previously shown that the early region of the bovine papillomavirus type 1 genome contains two nonoverlapping segments that can independently induce the morphological transformation of cultured cells. The transforming gene from the 5' end of the early region is encoded by the E6 open reading frame. The second transforming segment was previously localized to a 2.3-kilobase fragment (2.3T) from the 3' end of the early region. To determine which of the four open reading frames (E2, E3, E4, and E5) located within 2.3T encodes a transforming gene, we have now introduced a series of insertion and deletion mutations into a clone (pHLB1) in which 2.3T is activated by the Harvey viral long terminal repeat, and we tested the mutants for their ability to induce focal transformation. Our results indicate that the E5 open reading frame, which could encode a low-molecular-weight hydrophobic peptide, is required for pHLB1-induced transformation of NIH 3T3 cells, but that the E2, E3, and E4 open reading frames are not.

The bovine papillomavirus distal "enhancer" is not cis essential for transformation or for plasmid maintenance

We constructed a mutant of bovine papillomavirus type 1 (BPV-1) DNA that lacked a transcriptional enhancer located 3' to the polyadenylation site of the early viral RNAs expressed in transformed cells. This mutant DNA, when separated from the procaryotic sequences, transforms mouse cells with an efficiency comparable to that of the full BPV-1 genome, and it exists as a stable multicopy plasmid in transformed cells. The BPV-1 distal enhancer suppresses the effects of a cis-inhibitory element in pML2 sequences but is not essential for the expression of the viral genes involved in cellular transformation or plasmid maintenance.

Identification of the protein encoded by the E6 transforming gene of bovine papillomavirus

Papillomaviruses (PV) contain several conserved genes that may encode nonstructural proteins; however, none of these predicted gene products have been identified. Papillomavirus E6 genes are retained and expressed as RNA in PV-associated human and animal carcinomas and cell lines. This suggests that the E6 gene product may be important in the maintenance of the malignant phenotype. The E6 open reading frame of the bovine papillomavirus (BPV) genome has been identified as one of two BPV genes that can independently transform mouse cells in vitro. A polypeptide encoded by this region of BPV was produced in a bacterial expression vector and used to raise antisera. The antisera specifically immunoprecipitated the predicted 15.5-kilodalton BPV E6 protein from cells transformed by the E6 gene. The E6 protein was identified in both the nuclear and membrane fractions of these transformed cells.

Expression of a human U1 RNA gene introduced into mouse cells via bovine papillomavirus DNA vectors

We introduced a gene for human U1 small nuclear RNA, HU1-1, into mouse C127 cells via bovine papillomavirus (BPV) vectors. After transfection, up to 15% of the total U1 RNA in transformed cells was encoded by the introduced human genes. High levels of expression of the human gene were observed when the recombinant viral DNAs were maintained either as plasmids or after integration into high-molecular-weight DNA. As few as 400 and 35 base pairs of 5' and 3' flanking region sequences, respectively, were sufficient for transcription of human U1 RNA, and no increase in the level of expression was observed with HU1-1 DNA containing several kilobases of flanking region sequences. Several of the transformed cell lines contained the recombinant BPV DNA apparently integrated into the host genome. Integration or rearrangement or both of the U1-BPV DNA was promoted when the HU1-1 gene was positioned at the BamHI site downstream of the BPV transforming region. At least two variants of the U1-BPV DNAs were able to cause morphological transformation of cells despite the fact that these DNAs lacked a BPV transcriptional enhancer element.

Expression of a human U1 RNA gene introduced into mouse cells via bovine papillomavirus DNA vectors

We introduced a gene for human U1 small nuclear RNA, HU1-1, into mouse C127 cells via bovine papillomavirus (BPV) vectors. After transfection, up to 15% of the total U1 RNA in transformed cells was encoded by the introduced human genes. High levels of expression of the human gene were observed when the recombinant viral DNAs were maintained either as plasmids or after integration into high-molecular-weight DNA. As few as 400 and 35 base pairs of 5' and 3' flanking region sequences, respectively, were sufficient for transcription of human U1 RNA, and no increase in the level of expression was observed with HU1-1 DNA containing several kilobases of flanking region sequences. Several of the transformed cell lines contained the recombinant BPV DNA apparently integrated into the host genome. Integration or rearrangement or both of the U1-BPV DNA was promoted when the HU1-1 gene was positioned at the BamHI site downstream of the BPV transforming region. At least two variants of the U1-BPV DNAs were able to cause morphological transformation of cells despite the fact that these DNAs lacked a BPV transcriptional enhancer element.

Transcription control region within the protein-coding portion of adenovirus E1A genes

A single-base deletion within the protein-coding region of the adenovirus type 5 early region 1A (E1A) genes, 399 bases downstream from the transcription start site, depresses transcription to 2% of the wild-type rate. Complementation studies demonstrated that this was due to two effects of the mutation: first, inactivation of an E1A protein, causing a reduction by a factor of 5; second, a defect which acts in cis to depress E1A mRNA and nuclear RNA concentrations by a factor of 10. A larger deletion within the protein-coding region of E1A which overlaps the single-base deletion produces the same phenotype. In contrast, a linker insertion which results in a similar truncated E1A protein does not produce the cis-acting defect in E1A transcription. These results demonstrate that a critical cis-acting transcription control region occurs within the protein coding sequence in adenovirus type 5 E1A. The single-base deletion occurs in a sequence which shows extensive homology with a sequence from the enhancer regions of simian virus 40 and polyomavirus. This region is not required for E1A transcription during the late phase of infection.

A cloned human immunoglobulin heavy chain gene with a novel direct-repeat sequence in 5' flanking region

A rearranged human immunoglobulin gamma 1 heavy-chain gene (HIG1) was cloned from a human plasma cell leukemia cell line, ARH-77. The cloned gene possessed a unique direct repeat sequence of 84 bp in the 5' flanking region as well as an enhancer-like element in the JH-C gamma 1 intron. The latter sequence is located 1 kb downstream of 3' end of the J6 exon. The direct-repeat sequence in the 5'-flanking region contained a core-like sequence resembling that of viral enhancer elements. It is located in the intron between two leader exons. P1 nuclease mapping and exonuclease VII digestion experiments showed that most of the direct repeats are noncoding regions and spliced out from the transcript. These data suggested that HIG1 gene might have two kinds of enhancer-like elements at both sides of the V region gene. HIG1 gene has been introduced by the protoplast fusion into mouse myeloma cells (NSI and J558L cells) and mouse fibroblasts. A pSV2gpt vector containing HIG1 gene (pSV2-HIG1) was used to transform the cells. The amounts of mRNA synthesized in the transformed cells were at least 50 to 100 times larger than those in ARH-77 cells, although about one copy of HIG1 gene was present in DNA of a transformed cell. HIG1 gene was not expressed in fibroblasts, indicating that the enhancer of HIG1 gene acts in a tissue-specific manner but not in a species-specific one. The role of two kinds of enhancer-like elements in HIG1 gene is discussed in connection with the high-level expression of this gene in mouse myeloma cells.

Identification of a second transforming region in bovine papillomavirus DNA

Bovine papillomavirus type 1 (BPV-1) has been used as a model for studying papillomavirus genetics because BPV-1 virions or BPV-1 genomic viral DNA efficiently induce morphologic transformation of certain cultured cells. Previous studies of BPV-1-induced transformation have found that a cloned 5.4-kilobase (kb) fragment (69T) of the genome is transforming and that a 2.3-kb segment from the 3' end of this fragment is also transforming if activated by a retroviral regulatory element (the long terminal repeat). We now report that 69T contains another transforming segment near its 5' end that can also be activated by a long terminal repeat. Since this second segment does not overlap the 3' transforming segment, we conclude that BPV-1 encodes at least two genes that can independently transform cultured cells. Mutational analysis of the 5' transforming segment suggests that the transforming gene of this segment lies within the E6 open reading frame. The two transforming segments differ in their biological activity in that the E6-containing fragment can transform C127 mouse cells but not NIH3T3 mouse cells, whereas the 3' fragment can transform both cell lines.

A tissue-specific transcription enhancer element in the human immunoglobulin lambda light chain locus

An 8.0-kb EcoRI fragment of the human immunoglobulin (Ig) lambda light chain locus carrying the Ke-Oz- and Ke-Oz+ constant region genes and flanking sequences was studied for the presence of a transcriptional enhancer. Two types of assays were used. In the first, we measured the ability of recombinant plasmids carrying the 8.0-kb Ig fragment covalently linked to the aminoglycoside phosphotransferase (aph) gene to transform mouse myeloma or mouse fibroblast cells to geneticin resistance. In the second, we used RNA spot and Northern blot hybridization analyses to determine the relative levels of aph specific RNA transiently expressed after DNA transfection. In fibroblast cells, the transformation frequencies were independent of the presence of the Ig fragment in the vector and there was no difference in the level of transient expression of the aph gene. In myeloma cells, the Ig fragment enhanced at least 10-fold both the number of transformants and the level of aph gene expression over that obtained with vector alone. These results indicate the presence of a tissue-specific transcriptional enhancer in the 8.0-kb EcoRI fragment of the human Ig C lambda locus.

Effects of orientation and position on the activity of a herpes simplex virus immediate early gene far-upstream region

It has previously been shown that a far-upstream region of the herpes simplex virus immediate early (IE) gene 3 increases the expression of a linked thymidine kinase (TK) gene and also contains sequences which respond to stimulation of transcription by a virion component. The effects of altering the orientation and distance of the far-upstream region with respect to the normal IE gene 3 promoter are described. Reversal of the orientation whilst retaining the normal position of the far-upstream region did not affect its activity, but placing it downstream from the TK gene abolished any detectable effect. When the far-upstream region was separated from the promoter by insertion of Escherichia coli DNA fragments (approximately 1000 base pairs), its activity was reduced but not prevented. A similar effect was observed for unstimulated expression of TK and stimulated expression in the presence of the virion component. The IE gene 3 far-upstream region therefore resembles enhancer sequences in some respects but also shows significant differences.

Multiple enhancer domains in the 3' terminus of the Prague strain of Rous sarcoma virus

The 3' terminal region of the Prague strain of Rous sarcoma virus (PrRSV) contains at least three distinct domains that comprise two functional enhancer elements. Two of these domains (designated B and C) are found in the U3 region of the 3' long terminal repeat (LTR) while the third (designated A) is located in the sequences immediately preceding the LTR termed XSR sequences. Combinations of adjacent domains [e.g., (A + B or B + C)] are capable of activating the expression of the SV40 early promoter (21 bp repeats and TATA box) coupled to coding sequences from the prokaryotic gene chloramphenicol acetyltransferase (CAT) while a single domain is inactive. Furthermore, duplication or triplication of the central domain B restores activity. The related, Schmidt-Ruppin, strain of RSV, contains an almost identical 3' LTR element, but differs in the enhancer sequences immediately preceding the 3' LTR. A model is presented in which the sequence differences may contribute to the difference in disease spectrum of transformation defective (td) variants of these viruses.

A novel bovine papillomavirus (BPV-6) causing true epithelial papillomas of the mammary gland skin: a member of a proposed new BPV subgroup

A papillomavirus has been isolated from frond epithelial papillomas of the bovine udder. It is clearly distinguishable from all other bovine papillomaviruses (BPVs) based on DNA sequence homology and antigenic properties and is thus characterised as a new entity, designated BPV-6. BPV-6 does not possess the interspecific papillomavirus antigen, its genomic DNA (7.2 kb) is smaller than, and does not show any sequence homology to BPV-1, BPV-2, or BPV-5, whereas it is approximately the same length as BPV-3 or BPV-4, with which it shares some sequence homology. The bovine papillomaviruses have been classified into two subgroups: subgroup A, composed of BPV-1, BPV-2, and BPV-5, all of which induce fibropapillomas, and subgroup B, composed of BPV-3, BPV-4, and BPV-6, all of which cause true epithelial papillomas.

Short and long range activation by the SV40 enhancer

Activation of transcription by the SV40 enhancer decreases in an apparently biphasic manner when DNA sequences are interposed between the SV40 enhancer and either the homologous SV40 early or the heterologous conalbumin promoter elements. With increasing lengths of short DNA fragments (up to about 150 bp) activation of transcription decreases to less than 10% of the maximum. This short range effect is observed for both the SV40 early and conalbumin promoter elements and for either orientation of the SV40 enhancer. With the conalbumin promoter, increasing the length of the interposing DNA to 275 bp decreases activation to approximately 4%. Larger inserts, of 650 or 3737 bp, lead to an activation of 0.5%. However, in these recombinants, transcription is still activated at least 10 fold compared to an enhancerless recombinant. The implication of these results is discussed.

Transcription control region within the protein-coding portion of adenovirus E1A genes

A single-base deletion within the protein-coding region of the adenovirus type 5 early region 1A (E1A) genes, 399 bases downstream from the transcription start site, depresses transcription to 2% of the wild-type rate. Complementation studies demonstrated that this was due to two effects of the mutation: first, inactivation of an E1A protein, causing a reduction by a factor of 5; second, a defect which acts in cis to depress E1A mRNA and nuclear RNA concentrations by a factor of 10. A larger deletion within the protein-coding region of E1A which overlaps the single-base deletion produces the same phenotype. In contrast, a linker insertion which results in a similar truncated E1A protein does not produce the cis-acting defect in E1A transcription. These results demonstrate that a critical cis-acting transcription control region occurs within the protein coding sequence in adenovirus type 5 E1A. The single-base deletion occurs in a sequence which shows extensive homology with a sequence from the enhancer regions of simian virus 40 and polyomavirus. This region is not required for E1A transcription during the late phase of infection.

A stable bovine papillomavirus hybrid plasmid that expresses a dominant selective trait

We describe a bovine papillomavirus hybrid plasmid containing the neomycin resistance gene from Tn5 inserted into a mammalian cell transcriptional unit. This plasmid is maintained as a stable extrachromosomal element (20 to 100 copies per diploid genome) in mouse cells selected either for the transformed phenotype or for resistance to the aminoglycoside G418. Cells selected for G418 resistance initially display a flat, nontransformed phenotype before exhibiting the gross morphological characteristics of transformation. The delay in the appearance of the transformed phenotype indicated that some intracellular event or series of events subsequent to the establishment of transcriptionally active bovine papillomavirus 1 hybrid plasmid is required for the manifestation of the transformed phenotype.

Transcriptional regulation of a herpes simplex virus immediate early gene is mediated through an enhancer-type sequence

An enhancer-type sequence has been identified in the promoter region for the herpes simplex virus type 1 (HSV-1) immediate early (IE) mRNA 3. The enhancer-type activity is host cell dependent, being greater in human cells and Syrian hamster cells (the usual host cell for in vitro propagation of HSV) than in Chinese hamster or mouse cells. Enhancer activity is stimulated up to 10-fold after superinfection by tsK, a temperature-sensitive mutant of HSV-1. The induction of enhancer activity is independent of de novo protein synthesis, showing that trans-activation is effected by a component of the virion. We propose that trans-regulation of IE mRNA 3 is mediated through an enhancer-type sequence, and that this provides one explanation for previously described regulation of HSV IE mRNAs by virion components.

A stable bovine papillomavirus hybrid plasmid that expresses a dominant selective trait

We describe a bovine papillomavirus hybrid plasmid containing the neomycin resistance gene from Tn5 inserted into a mammalian cell transcriptional unit. This plasmid is maintained as a stable extrachromosomal element (20 to 100 copies per diploid genome) in mouse cells selected either for the transformed phenotype or for resistance to the aminoglycoside G418. Cells selected for G418 resistance initially display a flat, nontransformed phenotype before exhibiting the gross morphological characteristics of transformation. The delay in the appearance of the transformed phenotype indicated that some intracellular event or series of events subsequent to the establishment of transcriptionally active bovine papillomavirus 1 hybrid plasmid is required for the manifestation of the transformed phenotype.

The transforming function of bovine papillomavirus DNA

When bovine papillomavirus (BPV) or its 7.9-kilobase full viral DNA genome induces focal transformation of mouse cells, the viral DNA is maintained in the transformed cells as multiple episomal copies. This transforming capacity and maintenance of the episomal state previously has been localized to a 69% subgenomic fragment of the viral DNA genome. We now have characterized further the BPV DNA sequences that can encode the transforming function. We first created a series of BPV DNA deletion mutants and correlated the location of the deletions with the capacity of the deleted viral DNAs to induce transformation of mouse cells. The results indicated that two discontinuous segments of the viral DNA were required for transformation. One segment, near the 5' end of the 69% transforming fragment, probably represents a control element of the viral DNA. The second segment, which lies within the 3' end of the 69% fragment, encodes transforming sequences of the viral DNA; ligation of a retroviral control element (the long terminal repeat DNA of Harvey murine sarcoma virus) to the 2.3-kilobase segment at the 3' end of the 69% fragment induces transformation of mouse cells. In contrast to mouse cells transformed by the full-length BPV DNA genome, the cells transformed by the deleted BPV DNA genomes contained few viral DNA copies; at least some copies appeared to be integrated. We conclude that different viral functions mediate cellular transformation and maintain the viral DNA in its episomal state.