Identification of a DNA segment containing the human DNA polymerase alpha gene

We isolated a temperature-sensitive mutant from mouse FM3A cells, designated as tsFT20, the DNA polymerase alpha activity of which is heat-labile. A hybrid clone (M6-39 cells) between human cells and tsFT20 cells contained one or two human chromosomes. M6-39 cells (primary hybrid) were exposed to gamma-ray and re-fused with tsFT20, after which we isolated two temperature-resistant secondary hybrids, both of which retained an identical minute portion of the human chromosome, 400-500 kilobase pairs (kbp). Immunological studies demonstrated that this secondary hybrid expressed human DNA polymerase alpha. Thus, the human DNA polymerase alpha gene was located within a DNA region of 400-500 kbp.