methylnitronitrosoguanidine and 2-6-diaminopurine

Frequent mutation to adenine analog resistance in diploid human cells reflected heterozygosity for recessive alleles affecting expression of the adenine phosphoribosyltransferase (APRT) locus. Cells from both parents of APRT-deficient sibs were heterozygous and had rates of spontaneous mutation to 2,6-diaminopurine (DAP) resistance of 6.0 x 10(-5) and 16 x 10(-5) per cell generation. Spontaneous DAP-resistant mutants were not observed in cultures of homozygous cells. Almost all mutants of proven heterozygous cultures were APRT deficient and could not use adenine for growth. Frequent DAP-resistant mutations identified heterozygous strain 438, which carried an allele encoding a partially defective form of APRT. All DAP-resistant mutants of strain 438 were partially APRT deficient and could use adenine for growth. The frequency of MNNG-induced DAP-resistant mutants in homozygous strains was approximately the square of the induced frequency in heterozygous strains.

Topics: 2-Aminopurine; Adenine Phosphoribosyltransferase; Drug Resistance; Humans; Methylnitronitrosoguanidine; Mutation; Pentosyltransferases