DNA polymerase activity in a repair-deficient human cell line

A human low-density-lipoprotein (LDL) receptor-deficient diploid fibroblast cell line (GM1915) was determined to be short patch competent (DNA polymerase-beta) and long patch deficient (DNA polymerase-alpha) for DNA excision repair. Analysis of DNA from GM1915 cells or from WI38 control cells, following treatment with a mutagen known to initiate long patch excision repair, showed that GM1915 cells exhibited decreased resynthesis of oligonucleotide segments excised during repair. When cells deficient in DNA polymerase-alpha activity were permeabilized to permit LDL entry, repair synthesis immediately increased. These data suggest that DNA polymerase-alpha is not activated by mutagen treatment in GM1915 cells and that introduction of LDL into the cells results in activation of the enzyme.