Ribonucleotide reductase M2 subunit sequences mapped to four different chromosomal sites in humans and mice: functional locus identified by its amplification in hydroxyurea-resistant cell lines

The sites of sequences homologous to a murine cDNA for ribonucleotide reductase (RR) subunit M2 were determined on human and murine chromosomes by Southern blot analysis of interspecies somatic cell hybrid lines and by in situ hybridization. In the human genome, four chromosomal sites carrying RRM2-related sequences were identified at 1p31----p33, 1q21----q23, 2p24----p25, and Xp11----p21. In the mouse, M2 sequences were found on chromosomes 4, 7, 12, and 13 by somatic cell hybrid studies. By Southern analysis of human hydroxyurea-resistant cells that overproduce M2 because of gene amplification, we have identified the amplified restriction fragments as those that map to chromosome 2. To further confirm the site of the functional RRM2 locus, two other cDNA clones, p5-8 and S7 (coding for ornithine decarboxylase; ODC), which are coamplified with RRM2 sequences in human and rodent hydroxyurea-resistant cell lines, were mapped by Southern and in situ hybridization. Their chromosomal map positions coincided with the region of human chromosome 2 (p24----p25) that also contains one of the four RRM2-like sequences. Since this RRM2 sequence and p5-8 and ODC are most likely part of the same amplification unit, the RRM2 structural gene can be assigned to human chromosome 2p24----p25. This region is homologous to a region of mouse chromosome 12 that also carries one of numerous ODC-like sequences. In an RRM2-overproducing mouse cell line, we found amplification of the chromosome 12-specific restriction fragments. Thus, we conclude that mouse chromosome 12 carries the functional locus for RRM2.