Reacquisition of a functional early region by a mouse transformant containing only defective simian virus 40 DNA

Spontaneous rearrangement of integrated simian virus 40 DNA in nine transformed rodent cell lines

Frequencies of spontaneous DNA rearrangement within or near integrated simian virus 40 (SV40) DNA were measured in four transformed mouse and rat cell lines of independent origin and in five clones of the SV40-transformed mouse line SVT2. Rearrangements were detected as polymorphisms of restriction enzyme fragment length in subclones of the lines. At least 17% of the subclones of each line had detectable rearrangements. The rate of rearrangement was calculated to be at least 5 x 10(-3) events per cell per division. No rearrangements were detected in sequences of an immunoglobulin gene, part of the coding region of the mouse protein p53, and five proto-oncogenes. The possible role of recombination between duplicated segments of integrated SV40 DNA in generating rearrangements was studied in the five SVT2 clones, which differed in the number of duplications within a single SV40 DNA segment. The SVT2 clone that had no duplications, M3, became rearranged further at least as frequently as did closely related lines with one, two, or three duplications. Another line in this group that had one small duplication, X1, had a much higher frequency of rearrangement than did the others; integrated SV40 DNA of X1 became mostly rearranged within 100 cell divisions. The examples of M3 and X1 suggested that the high rate of rearrangement characteristic of integrated SV40 DNA was influenced more by the presence of particular sequences within or near integrated SV40 DNA than by the number or extent of duplicated sequences.

Comparison of the mouse P(1)450 gene and flanking sequences from a MOPC 41 plasmacytoma and normal liver

The murine P(1)450 gene is inducible by foreign chemicals such as dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin; TCDD). The induction process appears to involve binding of TCDD to the Ah receptor, interaction of the inducer-receptor complex with chromatin, and transcriptional activation of the P(1)450 gene. P(1)450 gene expression did not occur in the MOPC 41 plasmacytoma transplanted intra-abdominally in the BALB/c mouse. By Southern blot analysis, the P(1)450 gene restriction patterns are similar between MOPC 41 DNA and normal mouse liver DNA digested with Eco RI, Bam HI, or Hind III, suggesting there is no evidence for a gross chromosomal rearrangement in the tumor P(1)450 gene. The P(1)450 gene isolated from a genomic DNA library derived from the MOPC 41 tumor lacked the first exon and two-thirds of the first intron because of a rearrangement that presumably occurred during construction of the genomic DNA library. An unknown upstream segment of 2578 bases that had recombined with the remainder of the P(1)450 gene was sequenced and found to contain several repetitive sequences on both strands. The remaining 6272 bases of the P(1)450 gene (2532 bp of exons, 1969 bp of introns and 1771 bp of 3'-flanking region) are identical between the BALB/cJ-derived MOPC 41 and normal C57BL/6N mouse liver, with the exception of one CTTT repeat in the second intron. Hence, the BALB/c and C57BL/6 inbred mice, generally regarded as among the most divergent of Mus domesticus inbred laboratory strains, possess a P(1)450 gene and flanking region that exhibit greater than 99.9% similarity in nucleotide sequence.