MOUSE GENES ENCODING DNA TOPOISOMERASE-I

We have initiated a genetic analysis of the physiologically important enzyme type I DNA topoisomerase in mouse. The exon-intron structures o f the 5' part and the 3' part of the active gene, Top-1, were determin ed and shown to be quite similar to those of the previously determined human gene TOP1. The active mouse gene was mapped to the distal Chrom osome (Chr) 2. In addition, the mouse genome contains one truncated pr ocessed topoisomerase-I-related pseudogene (retroposon), Top-1ps, on C hr 16. The Top-1ps locus, together with the immunoglobulin-lambda-ligh t-chain locus, defines an additional conserved linkage group common to murine Chr 16 and human Chr 22, the site of the human pseudogene TOP1 P2. The mapping data suggest that the pseudogene was established befor e mammalian radiation. Structural features, shared by the mouse and th e human pseudogene, support this possibility.