Absence of mutations in the functional parts of the p120-GAP gene in carcinogen-induced mouse liver tumors

The GTPase activating proteins (GAP) stimulate the intrinsic GTPase activity of ras-p21 thus converting the protein into its inactive form. We have now analyzed carcinogen-induced mouse liver tumors for the possible occurrence of mutational changes in one of the two known GAP genes, namely p120-GAP. RNA from a total of 21 tumors was reverse transcribed by use of GAP-specific primers, amplified by PCR and sequenced. All known functional domains of p120-GAP were included into the analysis. None of the liver tumors analyzed was found to be mutated within these regions of the gene. Moreover, Southern blot analysis of the gene did not reveal any structural changes. However, at five positions we discovered deviations from the published mouse fibroblast sequence, including two mouse strain-specific sequence polymorphisms.