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Biomedical subjects

K Chowdhury

Publications and source records attributed to K Chowdhury.

At least 73 records · Page 4Linked to original sources
PubMed1983

Interaction of nogalamycin with chromatin.

Number of available nogalamycin binding sites in Sarcoma-180 chromatin is less than that present in Sarcoma-180 DNA. Gradual removal of proteins from chromatin by salt leads to increase in available drug binding sites, without appreciable alteration in binding affinity. Histones restrict the accessibility of nogalamycin to chromosomal DNA, whereas high mobility group (HMG) proteins have no effect. Association of histone H1 with chromosomal DNA has a more marked inhibitory effect on nogalamycin binding than other types of histones. Chromosomal protein induced conformational change in DNA appears to be the main factor in determining the availability of strong binding sites.

Chromatin↗
PubMed1983

Structural analysis of integrated polyomavirus DNA in a polyomavirus-induced hamster tumor cell line.

The nucleotide sequence and structural organization of integrated polyomavirus DNA and flanking host chromosomal DNA in a polyomavirus-induced hamster tumor cell line were evaluated. Although the proximal portion of the early transcriptional region was intact, the remainder of the integrated viral sequences was characterized by a series of rearrangements, including deletions, insertions, and a tandem duplication. Short direct repeats of different nucleotide sequences located on each side of the host-viral DNA junctions we examined were observed. Tumor cell chromosomal DNA flanking the integration site contained regions of patchy homology with viral DNA sequences which could have participated in the recombinational events leading to stable integration. The presence of several unusual structural features of tumor cell chromosomal DNA at the site of viral DNA integration, which were reminiscent of papovavirus DNA integrated into transformed cells, suggests that the recombinational mechanisms operative in vivo are accurately reflected by those functioning in vitro.

Animals↗
PubMed1982

Beta-hexosaminidase activities and isoenzymes in normal human ovary and ovarian adenocarcinoma.

Levels and isoenzyme profiles of beta-hexosaminidase were compared in extracts from normal ovarian and ovarian epithelial tumors. The specific activities of beta-hexosaminidase were significantly (P less than 0.001) higher in malignant than in normal ovarian tissues. The enzyme levels of the tumors depended on their degree of differentiation. Well-differentiated tumors had activities in the normal range, while poorly differentiated ones had values higher than the normal mean +/- 2 SD. The moderately and moderately to poorly differentiated tumors had intermediate levels. DEAE-cellulose chromatography was used to resolve the isoenzyme of beta-hexosaminidase. Two major forms, beta-hexosaminidase A and beta-hexosaminidase B, were detected in all the preparations. In one tumor specimen, a component eluting slightly ahead of beta-hexosaminidase A was also detected. For quick separation, a batch-wise procedure using DEAE-cellulose was adapted. Proportions of the isoenzymes A and B separated by batch-wise procedure were similar to those obtained by column chromatography. Heat stability, optimum pH, acid stability and substrate specificity of the beta-hexomsaminidase isoenzymes from ovarian tissues were similar to those from other human sources. Isoenzymes from tumor extracts were more labile to heat and acid pH compared with those from normal source. Slight differences in the affinity for the substrate p-nitrophenyl-beta-N-acetyl-galactosaminidase between the isoenzymes from normal and malignant ovaries were noted.

Acetylgalactosamine↗
PubMed1982

Isolation and characterization of polyoma virus mutants which grow in murine embryonal carcinoma and trophoblast cells.

Mouse trophoblast cell lines established from cultured midterm placenta and a cell line obtained from cultured blastocyst resemble trophectoderm cells. These cells are resistant to infection by wild-type polyoma virus. We have isolated six polyoma virus mutants capable of growing in trophoblast cell lines. Restriction enzyme analyses and marker rescue experiments revealed that the genetic changes necessary for the growth of these mutants ( PyTr mutants) in trophoblast cells were located in a regulatory region of the genome between the origin of viral DNA replication and the region encoding the viral structural proteins. PyTr mutants are, therefore, similar to PyEC mutants, described by others, which are able to grow in embryonal carcinoma cell lines such as F9 or PCC4. The nucleotide sequence of two independently obtained PyTr mutants has an identical 26-bp deletion from nucleotide 5131 to 5156. This deleted region is replaced by either the sequence GGGA or by viral DNA sequences that flank this deletion. PyECF9 mutants grow well in trophoblast and trophectoderm cells, but PyTr mutants do not grow in F9 or PCC4 cells.

Animals↗
PubMed1982

Stability of polyoma DNA sequences and virus-coded proteins during tumor formation.

To determine the stability of polyoma viral DNA in transformed rat cells during their growth in vivo, we compared the state and arrangement of polyoma virus DNA sequences in virus-transformed rat cell lines before and after their passage in vivo. In cell lines from 12 independent tumors induced by the inoculation of animals with three different transformed cell lines, we could detect no significant changes in the arrangement of viral DNA sequences associated with the in vivo passage of these cell lines. In 13 of 14 tumor cell lines examined, the pattern of polyoma virus tumor antigens, characterized by the presence of the polyoma virus large, middle, and small tumor antigens, was unchanged.

Animals↗
PubMed1980

Polyoma large tumor antigen is not required for tumorigenesis mediated by viral DNA.

The arrangement of viral DNA sequences in a hamster cell line derived from a tumor induced by a recombinant plasmid DNA preparation containing the entire polyoma virus genome was examined. In the recombinant plasmid employed, viral DNA sequences specifying the large species of polyoma tumor antigen but not the small and middle tumor antigens were interrupted by the insertion of plasmid DNA at the EcoRI restriction endonuclease site. Blot-hybridization analyses of tumor cell DNA indicated that the "joints" linking viral and plasmid DNAs in the original recombinant plasmid used in animal inoculation had been preserved. Integration into the hamster cell genome had apparently occurred within plasmid DNA sequences. These results indicate that polyoma large tumor antigen is not required for tumorigenesis mediated by viral DNA.

Animals↗
PubMed1980

A cloned polyoma DNA fragment representing the 5' half of the early gene region is oncogenic.

The two polyoma DNA fragments generated by cleavage with BamHI and EcoRI were cloned in pBR322, and their oncogenic potential was tested in vivo and in vitro. Only recombinant plasmid DNA containing a polyoma DNA fragment which extends clockwise from 58 to 0 map units and include approximately the 5'-proximal half of the early gene region produced tumors in newborn hamsters and transformed rat embryo cells in tissue culture. Southern blotting analysis indicated that the entire 2.2-kilobase polyoma BamHI-EcoRI fragment was intact in both a tumor cell line and a cell line transformed in culture which we examined. The presence of polyoma middle and small T antigen in these lines was demonstrated by immunoprecipitation and tryptic peptide mapping. DNA from a recombinant plasmid containing a polyoma genome deleted between 90 and 4 map units failed to induce tumors or transform cells.

Animals↗
PubMed1980

Cloned human polyomavirus JC DNA can transform human amnion cells.

The genome of the human polyomavirus JC (Mad-1 strain) was molecularly cloned in Escherichia coli by using the plasmid vector pBR322. Recombinant DNA molecules were constructed with the entire JC genome inserted either at its unique EcoRI site at 0.0 map units or at its unique BamHI site at 0.51 map units. Viral DNA from each of these recombinant plasmids was capable of transforming human amnion cells, and cell lines established from transformed foci were positive for JC tumor antigen as assayed by indirect immunofluorescence.

Amnion↗
PubMed1978

Origin of DNA replication in papovavirus chromatin is recognized by endogenous endonuclease.

Isolated simian virus 40 (SV40) and polyoma nucleoprotein complexes contain endonuclease that, under in vitro conditions, converts part (up to 30%) of the covalently closed superhelical DNA to full-length linear rods. The positions of the cleavage sites within the genomes of SV40 and polyoma were determined by digestion with various single-cut restriction endonucleases and subsequent agarose gel electrophoresis of the cleavage products. Both SV40 and polyoma covalently closed superhelical DNA were cleaved open at their respective origins of DNA replication (+/- 75 base pairs). The full-length linear DNA rods whose ends map adjacent to the origin of DNA replication could also be isolated by sodium dodecyl sulfate/phenol extraction both from SV40-infected permissive cells and from purified SV40 virions. These data reveal the presence of a unique structure of the papovavirus chromatin close to the initiation site of DNA replication.

Chromatin↗