Two different factors bind to the alpha-domain of the polyoma virus enhancer, one of which also interacts with the SV40 and c-fos enhancers.

Two nuclear factors from mouse 3T6 cells bind to a 22-bp segment constituting the alpha-domain of the polyoma virus enhancer. Binding of each factor can be competed out selectively by the appropriate double-stranded oligonucleotide, indicating that this binding is not strictly cooperative. Sequence homology between the two binding sites and the similar size of the protected regions may indicate that both factors, PEA1 and PEA2, are closely related. The binding site of PEA1 is centered on a sequence showing strong homology to the SV40 enhancer, the binding site of PEA2 is located immediately adjacent to it and shows a strong homology to the c-fos enhancer. Surprisingly, both SV40 and c-fos enhancers interact with PEA1, probably due to the presence of an extra base pair relative to c-fos in the PEA2 site. Factor PEA1 is probably identical to the recently described activator protein 1 (AP1).     

An SV40 "enhancer trap" incorporates exogenous enhancers or generates enhancers from its own sequences

We have transfected monkey CV-1 cells with non-infectious, linear SV40 DNA, lacking the 72 bp repeat enhancer region. Infectious virus was recovered from this "enhancer trap" upon cotransfection with enhancer DNA segments from various viruses, notably a truncated polyoma enhancer that was integrated as a dimer. Cotransfection of the "enhancer trap" with fragmented DNA of mouse, monkey, or human origin yielded no recombinant virus with integrated cellular sequences, with one possible exception. In some transfection experiments without added viral enhancer DNA, SV40 variants were generated that have a segment of their flanking "late" DNA duplicated to substitute for the deleted 72 bp repeat. In one variant, an 88 bp duplication creates a strong enhancer from this nonenhancing DNA region. Both the polyoma enhancer fragment and the spontaneously created enhancers lack the alternating purines-pyrimidines or "CACA box" suggested to be characteristic for enhancer elements and show only limited homology to the "GTGG(AAATTT)G box."     

Isolation and characterization of a protein fraction that binds to enhancer core sequences in intracisternal A-particle long terminal repeats

The U3 region of mouse intracisternal A-particle (IAP) long terminal repeats (LTRs) contains several nuclear protein-binding domains. Two of these contain sequences with homology to the SV40 enhancer core. We refer to these two domains as Enh1 and Enh2. The Enh2 domain is an important determinant of promoter activity in vivo. We report here the isolation of nuclear fractions from human 293 and mouse MOPC-315 cells which interact with Enh1 and Enh2. Purification was achieved via DNA-affinity chromatography on a multimerized oligonucleotide representing the Enh2 region from the LTR of the mouse genomic IAP element, MIA14. Glycerol gradient sedimentation suggested a native Mr of approximately 80-100 for the binding component(s) in both crude and affinity-purified fractions. UV cross-linking showed that the binding activity involved two polypeptides within this size range. The affinity-isolated fraction from each cell line was highly purified, as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and in vitro binding analysis. Exonuclease III footprinting showed that the two polypeptides interacted preferentially with the Enh1 and Enh2 domains within a 139-base pair segment from the MIA14 LTR. The polypeptides interacted in a sequence-specific manner with oligonucleotides representing these domains within the IAP LTR and with oligonucleotides containing the enhancer core sequence from SV40 and polyoma virus. Equilibrium binding studies indicated that the apparent dissociation constants for the polypeptides binding to the enhancer core sequence from MIA14, SV40, and polyoma virus were similar. Therefore, this affinity-purified fraction may represent a novel enhancer core-binding component which is distinct from the previously characterized rat CCAAT/enhancer-binding protein, C/EBP.     

Characterization of a cell type-specific enhancer found in the human papilloma virus type 18 genome.

We have previously isolated long-range acting enhancer elements from the HeLa genome by functional selection. In this report, the structural and functional characteristics of one (GA1) of the enhancers are reported. By cloning various restriction fragments and by deletion mutagenesis, the activity of GA1 was located in a 230-bp region. The nucleotide sequence of GA1 and genomic Southern blot analysis indicated that GA1 is derived from human papilloma virus (HPV) 18 DNA that had been integrated into the HeLa genome. The enhancer is located in the non-coding region of the HPV 18 genome. The HPV 18 enhancer consists of two functional domains, both of which have full enhancer activity in HeLa cells. The enhancer does not contain enhancer core sequences but contains several blocks of potential Z-DNA sequence. Like SV40 and polyoma virus enhancers, the activity of the HPV 18 enhancer was repressed by adenovirus E1a products. The HPV 18 enhancer shows a narrow cell type specificity: it is active in some cervical carcinoma cell lines, but inactive in all non-cervical cells except for one neuroblastoma cell line. These results suggest that the HPV 18 enhancer plays an important role in regulation of the viral genes.     

Comparison of CMV, RSV, SV40 viral and Vlambda1 cellular promoters in B and T lymphoid and non-lymphoid cell lines.

Determining the activity of viral and cellular regulatory elements in B or T lymphoid cell lines would facilitate appropriate utilization of the regulatory sequences for gene transfer- and expression-dependent applications. We have compared the activity of the CMV, RSV and SV40 viral promoter/enhancers as well as the Vlambda1 cellular promoter, in three B cell lines (REH, SMS-SB, C3P), three T cell lines (CEM, Jurkat, ST-F10), and two non-lymphoid cell lines (K-562, HeLa) using the luciferase reporter gene. In B cell lines, the activity of the CMV promoter/enhancer construct was the highest ranging from 10- to 113-fold greater than that of SV40. In contrast, in T cell lines the RSV promoter/enhancer activity was 11-65-fold higher than that of SV40. The Vlambda1 promoter activity was close to that of SV40 promoter/enhancer in most of the cell lines tested. We conclude that CMV and RSV promoter/enhancers contain stronger regulatory elements than do the SV40 and Vlambda1 for expression of genes in lymphoid cell lines.     

Xrep, a plasmid-stimulating X chromosomal sequence bearing similarities to the BK virus replication origin and viral enhancers.

The human X chromosome-linked fragment, "Xrep," was sequenced because it exerts a positive effect on plasmid growth in both E. coli and Saccharomyces cerevisiae. The sequence revealed three features similar to the human BK virus replication origin: Xrep has a true palindrome, CCTCC(T)3CCTCC, which is similar to "true" palindrome-like sequences found at the replication origins of polyoma [CCTC(T/C)10CTCC], BK [CCTC(A/G)8CCTCC] and SV40 [CCTCC(A)6GCCTCC] viruses. Twenty nucleotides away from the true palindrome, Xrep has the sequence GAATCCTATTCACTTTT while BK virus, the human analogue of SV40, has GAAATCCCTATTCTTTT in exactly the same position relative to the true palindrome. These two 17-mers differ only in the positions of two nucleotides comparing Xrep and BK virus. Also similar to the replication origins of DNA viruses, Xrep appears to have a cluster of enhancers adjacent to the origin-like sequences. Potent enhancer-like activity was detected in pSV1 X CAT/Xrep constructs. Xrep may originate from an endogenous virus, or from an X chromosomal replication origin.     

Common features of polyomavirus mutants selected on PCC4 embryonal carcinoma cells.

The genomic rearrangements of six polyomavirus mutants selected on PCC4 embryonal carcinoma cells have been compared and their common characteristics pointed out. All mutants show a duplication which includes at least the adenovirus type 5 (Ad5) E1A-like enhancer core sequence plus a deletion of variable size and location. The presence of the second enhancer core sequence, the SV40-like enhancer, is not required for expression of the PyEC PCC4 phenotype. Two of these mutants are also able to express polyomavirus T antigen on F9 and LT1 cells. Multiadaptation seems to require the duplication of the Ad5 E1A-like core sequence, the maintenance of the SV40-like core sequence and a local change in DNA stability.     

In vitro tumoricidal activity of macrophages against virus-transformed lines with temperature-dependent transformed phenotypic characteristics.

The susceptibility of targets to destruction by tumoricidal rat and mouse macrophages was studied with virus-transformed cell lines in which various elements of the transformed phenotype are only expressed at specific temperatures. BHK cells transformed by the ts3 mutant of polyoma virus, rat embryo 3Y1 cells transformed by a temperature-sensitive A cistron mutant of simian virus 40 (SV40) and the ts-H6-15 temperature-sensitive line of SV40-transformed mouse 3T3 cells were killed in vitro by macrophages at both the permissive (33 °C) or nonpermissive (39 °C) temperatures for expression of the transformed phenotype. 3T3, 3Y1 and BHK cells transformed by wild-type SV40 or polyoma virus were also destroyed by tumoricidal macrophages at both 33 and 39 °C, but untransformed 3T3, 3Y1, and BHK cells were not. Thus, transformed cells are killed by macrophages regardless of whether or not they express cell surface LETS protein or Forssman antigen, display surface changes which permit agglutination by low doses of plant lectins, express SV40 T antigen, have a low saturation density, or exhibit density-dependent inhibition of DNA synthesis.     

Transient expression of murine interferon-alpha genes in mouse and monkey cells

The coding regions of murine interferon-alpha (IFN-alpha) genes were combined with promoter and 3'-noncoding sequences from other eukaryotic genes. Transient expression of these fusion genes was achieved in monkey COS cells and in a mouse cell line (TOP cells) expressing polyoma virus (Py) large T antigen constitutively. The efficiency of the different expression plasmids was determined by measuring the amount of IFN secreted into the medium. Replacement of the 3'-noncoding region of an IFN-alpha gene by that of the rabbit beta-globin gene resulted in a fourfold higher IFN-alpha production. The SV40 early promoter and the Moloney murine leukemia virus (MoMLV) long terminal repeat (LTR) produced similar amounts of IFN-alpha in COS cells. However, a tandem combination of the SV40 enhancer/early promoter and the mouse metallothionein-I promoter appeared fivefold more active than the SV40 early promoter. In TOP cells the MoMLV LTR was found to be threefold more active than the Py early promoter.     

Nucleoprotein Complexes Containing Replicating Simian Virus 40 DNA: Comparison with Polyoma Nucleoprotein Complexes

Procedures for isolating nucleoprotein complexes containing replicating polyoma DNA from infected mouse cells were used to prepare short-lived nucleoprotein complexes (r-SV40 complexes) containing replicating simian virus 40 (SV40) DNA from infected monkey cells. Like the polyoma complexes, r-SV40 complexes were only partially released from nuclei by cell lysis but could be extracted from nuclei by prolonged treatment with solutions containing Triton X-100. r-SV40 complexes sedimented faster than complexes containing SV40 supercoiled DNA (SV40 complex) in sucrose gradients, and both types of SV40 nucleoprotein complexes sedimented ahead of polyoma complexes containing supercoiled polyoma DNA (py complex). The sedimentation rates of py complex and SV40 complex were 56 and 61S, respectively, based on the sedimentation rate of the mouse large ribosomal subunit as a marker. r-SV40 complexes sedimented as multiple peaks between 56 and 75S. Sedimentation and buoyant density measurements indicated that protein is bound to all forms of SV40 DNA at about the same ratio of protein to DNA (1-2/1) as was reported for polyoma nucleoproteins.