Viable deletion mutant of human papovavirus BK that induces insulinomas in hamsters.

A plaque morphology mutant (pm-522) of human papovavirus BK, which was rescued from a human papovavirus BK-induced hamster pineocytoma, was characterized and compared with a cloned wild-type virus (wt-501). Mutant pm-522 formed turbid plaques and grew more slowly than wt-501 in human embryonic kidney (HEK) cells. The immunofluorescence assay revealed that more HEK cells underwent abortive infection with pm-522 than with wt-501. Whereas wt-501 induced brain tumors and osteosarcomas, but no insulinomas, in hamsters, pm-522 induced brain tumors and insulinomas. The DNA of pm-522 was found by electrophoresis and electron microscopy to have a deletion (85 +/- 15 base pairs) and an insertion (40 +/- 10 base pairs) between map coordinates 0.708 and 0.725 from the endonuclease EcoRI cleavage site. These results demonstrate the presence of a viable deletion human papovarivus BK mutant capable of inducing insulinomas in hamsters.     

Change of DNA near the origin of replication enhances the transforming capacity of human papovavirus BK.

A turbid-plaque-forming mutant (pm522) of human papovavirus BK, which has a small deletion at about 0.7 map unit and grows somewhat more slowly in human cells than does wild-type BK virus, transformed hamster and rat cells in culture much more efficiently than did wild-type virus. Another plaque morphology mutant, pm525, forming turbid plaques larger than those of pm522 also had a high transforming capacity. The similar difference in transforming capability between wild-type and plaque morphology viruses was observed with DNAs extracted from virions. Recombinant viruses were constructed from the wild-type DNA fragment lacking HindIII-C (0.62 to 0.73 map unit) and pm522 HindIII-C (including the origin of replication) by the molecular cloning method. Characterization of the recombinants showed that the change near the origin of DNA replication was responsible both for the altered plaque morphology and for the enhanced transforming capacity of the BK virus mutant.     

Expression of viral early functions in rat 3Y1 cells infected with human papovavirus BK.

A plaque morphology mutant (pm-522) of BK virus (BKV) with a small deletion at map unit 0.72 can readily transform rat 3Y1 cells, but wild-type BKV (wt-501) cannot. We examined the expression of the viral early functions in BKV (wt-501 or pm-522)-infected 3Y1 cells within a 2-week period after infection, before foci of transformed cells became detectable, to know how the difference between the two BKVs occurs. After a high-multiplicity infection, comparable amounts of free viral DNA (forms I and II) were found by Southern blotting analyses to persist in the nuclei of the cells infected with wt and pm BKVs. Whereas the proportion of T antigen-positive cells, as revealed by the indirect immunofluorescence method with complement, remained at a level of 60% in pm BKV infection, the level of T antigen-positive cells in wt BKV infection decreased from the initial 45% to 1% on day 9. The results obtained by the immunoprecipitation analyses of radiolabeled proteins from the infected cells were consistent with the immunofluorescence data. Viral early mRNA was detectable on day 2 and increased on day 9 in pm BKV infection, but in wt BKV infection, the low level of early mRNA detected on day 2 disappeared on day 9. Cell DNA synthesis and cell growth were enhanced more in pm BKV infection than in wt BKV infection. The low level of viral DNA synthesis that occurred in the infected rat cells was more prominent in pm BKV infection than in wt BKV infection. These data indicate that the expression of viral early functions continued much longer in pm BKV-infected rat cells than in wt BKV-infected rat cells, where the expression was probably repressed soon after infection. Continued T antigen production directed by the unintegrated viral genomes appears to be required for efficient transformation of rat cells by BKV.     

Isolation of an integrated provirus of Moloney murine leukemia virus with long terminal repeats in inverted orientation: integration utilizing two U3 sequences.

We have previously described the construction of a mutant of Moloney murine leukemia virus, in594-2, which carries a 2-base-pair insertion in the U5 region of the genome and is partially defective in forming the integrated proviral DNA. We have now recovered a cloned copy of an unusual provirus from rat cells infected with this mutant. The viral genome is flanked by long terminal repeats in inverted orientation, with U3 sequences joined to cellular DNA at both of the outer edges. In addition, the provirus is a recombinant, containing a segment of a VL30 element in inverted orientation in place of the Moloney murine leukemia virus env region. The recovery of this provirus indicates that two U3 regions can be used for viral integration and suggests that there may be no absolute requirement in the reaction for those U5 sequences outside the 13-base-pair inverted repeats.     

Enhancement of the transforming capacity of BK virus by partial deletion of the 68-base-pair tandem repeats.

We constructed a set of deleted BK viral DNAs that lack part of the triplicated 68-base-pair (bp) sequences (the central unit has an 18-bp deletion) and assayed them for capacity to transform hamster kidney cells. Deletion of one of the two 68-bp units remarkably enhanced transforming capacity.     

Naturally occurring BK virus variants (JL and Dik) with deletions in the putative early enhancer-promoter sequences.

The genomes of two independently isolated BK virus (BKV) variants (JL and Dik) were compared with prototype BKV DNA by restriction endonuclease mapping and sequence analysis. Differences were mainly detected in two regions: the BKV (JL) and BKV (Dik) putative early enhancer-promoter regions and the middle of the T-antigen-coding regions. Base sequence analysis of these two regions showed the following. (i) The putative enhancer-promoter regions of BKV (Dik) and BKV (JL) contained only one 68-base-pair (bp) unit of the 68-bp triplication (the central copy of which is missing 18 bp) present in prototype BKV. (ii) In the same region, BKV (JL) and BKV (Dik) contained unique stretches of DNA 33 and 63 bp long, respectively. In these 63 bp, a sequence which was very similar to the proposed simian virus 40 enhancer core sequence (GGAGTGGAAAG) was present. (iii) The altered restriction endonuclease recognition sites in the sequenced part of the T-antigen-coding region of BKV (JL) and BKV (Dik) were due to base sequence changes, leaving the amino acid sequence unchanged.     

Arrangement of the genome of the human papovavirus RF virus.

DNA from plaque-purified RF virus, a variant of BK virus, was found to contain two species of molecules. Hybridization of each DNA species to the fragments of BK virus DNA revealed that one species had a deletion corresponding to at least 50% of the late region and the other had a deletion corresponding to at least 40% of the early region of BK virus DNA. Analysis by cleavage of each RF virus DNA species with restriction endonucleases EcoRI, HindIII, AvaII, and PvuII, when compared with BK virus DNA, revealed that the size and number of fragments were different. These results suggest the loss of some restriction sites and the appearance of new sites, probably as a result of base changes in each RF virus DNA species. Furthermore, analysis of the restriction map of each DNA molecule revealed in insertion(s) in both DNA species.     

Role of specific simian virus 40 sequences in the nuclease-sensitive structure in viral chromatin.

A nuclease-sensitive region forms in chromatin containing a 273-base-pair (bp) segment of simian virus 40 DNA encompassing the viral origin of replication and early and late promoters. We have saturated this region with short deletion mutations and compared the nuclease sensitivity of each mutated segment to that of an unaltered segment elsewhere in the partially duplicated mutant. Although no single DNA segment is required for the formation of a nuclease-sensitive region, a deletion mutation (dl45) which disrupted both exact copies of the 21-bp repeats substantially reduced nuclease sensitivity. Deletion mutations limited to only one copy of the 21-bp repeats had little, if any, effect. A mutant (dl135) lacking all copies of the 21- and 72-bp repeats, while retaining the origin of replication and the TATA box, did not exhibit a nuclease-sensitive region. Mutants which showed reduced nuclease sensitivity had this effect throughout the nuclease-sensitive region, not just at the site of the deletion, indicating that although multiple determinants must be responsible for the nuclease-sensitive chromatin structure they do not function with complete independence. Mutant dl9, which lacks the late portion of the 72-bp segment, showed reduced accessibility to BglI, even though the BglI site is 146 bp away from the site of the deletion.     

The T/t common region of simian virus 40 large T antigen contains a distinct transformation-governing sequence.

Simian virus 40 large T antigen (T) can transform cultured cells, but the mechanisms by which it functions are not entirely understood. Several lines of evidence have suggested that the amino-terminal approximately 130 residues of T may be sufficient to confer the transforming capability. Oligonucleotide-directed mutagenesis was used to generate a series of deletion and substitution mutants within the amino-terminal 82 residues of T, the segment which is shared with simian virus 40 small t antigen (t). Results of stability and transformation assays of these mutants strongly suggest that the 1-to-82 region of T contains sequences which govern T transforming activity and affect in vivo stability. Instability and a defect in transforming activity could be separated from one another genetically. Thus, the 1-to-82 region appears to contain a specific region that contributes to the transforming function of the protein. This segment operates by means other than the simple binding of pRb and/or p107.     

Amplification of a mitochondrial DNA sequence in the cytoplasmically inherited 'ragged' mutant of Aspergillus amstelodami

A comparison has been made between mtDNA of the cytoplasmically inherited 'ragged' mutant of Aspergillus amstelodami and that of the wild-type strain. Ragged mitochondria contain both the wild-type mitochondrial genome and several large DNA molecules which are not cleaved by the restriction endonucleases BamHI, HaeIII, HhaI, HindII, HindIII, PstI and MboI, but are converted by either EcoRI or HpaII into a single 820-840 base-pair fragment. Restriction analysis and molecular hybridization data indicate that this fragment contains sequences of wild-type mtDNA located within a 1200-base-pair segment of the 40,500-base-pair genome, for which a basic restriction map has been deduced. It is concluded that in the ragged mutant a small segment of wild-type mtDNA has been amplified as tandem repeats, which is reminiscent of the Rho- petite phenotype of yeast. The results are discussed in relation to the phenomenon of senescence in Podospora anserina.     

Comparative analysis of GS and BK virus genomes.

Analysis of heteroduplexing between the genomes of GS virus, a BK-group virus, and the prototype BK virus revealed one region of nonhomology. Further analysis by cleavage of viral DNA with the restriction endonucleases EcoRI, HindIII, and HaeIII revealed that base changes in the GS virus genome spanned 0.6 to 0.7 map unit from the EcoRI site. Large T and small t antigens of GS virus appear to be similar in size to the BK virus antigens.