Identification of marker chromosomes by in situ hybridization technique using alpha and "classical" satellite DNA probes with relative chromosomal specificity.

Nine additional marker chromosomes in children with mental retardation and congenital malformation were investigated by routine cytogenetic and in situ hybridization techniques. Five metacentric non-satellited markers and four satellited markers of unknown origin were determined by routine and banding staining. To determine the origin of small marker chromosomes a special scheme involving the sequential application of definite alphoid and "classical" satellite DNA probes with the relative chromosome specificity was employed. The probes specific to four groups of definite chromosomes (i) 1, 3, 5, 6, 7, 10, 12, 16, 19; (ii) 2, 4, 8, 9, 13, 14, 15, 18, 20, 21, 22; (iii) 1, 11, 17, X; (iiii) 9, 13, 14, 15, 21, 22, Y and in situ hybridization under low stringency conditions were used at the first stage of experiments. After the preliminary analysis and the determination of possible origin of a marker chromosome from a definite group of chromosomes the probes with a strong chromosome-specificity under high stringency conditions were used. The approach involving the application of the original collection of chromosome-specific DNA probes, including molecular markers to practically all human chromosomes [1, 2], and various conditions of hybridization provides an effective method for detecting unknown markers. Marker chromosomes investigated in this study were derivatives of chromosomes 7, 9 (two cases), 13, 14, 21 (two cases), X and Y.

The oncogene of BAV-3 as a mutagen.

We studied the mutagenic and carcinogenic effects on mammalian cells of two EcoRI DNA fragments of bovine adenovirus type3 (BAV-3) integrated into the pBR325 plasmid. Fragment D located between 3.6 and 19.7 map units, contains the viral oncogene, fragment C, located between 44.3 and 63.7 map units, has no oncogenic activity. The BAV-3 oncogene was shown to increase significantly the frequency of 6-mercaptopurine (6MP)-resistant mutants in Chinese hamster calls. Fragment C, pBR325 without viral sequences and DNA from normal Syrian hamster cells did not have any mutagenic effect. We also looked at the combined action of the viral DNA fragments and the tumour promoter 12-O-tetradecanoylphorbol-13-acetate (TPA), which enhances the transforming effect of carcinogens. TPA was shown to increase the mutant yield on exposure to the viral oncogene but not to induce mutagenic activity in those types of DNA that are unable to transform cells. Probably TPA does not affect the initiation of the mutation process, but acts on later stages just as it affects carcinogenic activity. Thus the results obtained confirm the existence of parallelism between the mutagenic and transforming effects of viral DNA and show that both activities are mapped in the same region of viral DNA - its oncogene.