Purine Synthesis and Excretion in Mutants of the WI-L2 Human Lymphoblastoid Line Deficient in Adenosine Kinase (AK) and Adenine Phosphoribosyltransferase (APRT)

Abstract

Human lymphoblasts offer several advantages over fibroblasts for the study of mutations which affect purine metabolism in human cells in tissue culture. Because fibroblasts become senescent after a more or less finite number of doublings, a mutant once selected and cloned offers limited material for detailed biochemical analysis. Lymphoblasts divide indefinitely so that one may repeatedly obtain sufficient quantities of cloned mutants for biochemical study. An additional advantage is that although these lines maintain their karyotype in culture (1,2), they can with continued passage accumulate a high frequency of spontaneous mutations in genes which are not essential for survival. We have found the frequency with which mutations in some autosomal genes occur in the WI-L2 line of human splenic lymphoblasts (3) in some cases approaches that for X-linked genes, such as hypoxanthine-guanine phosphoribosyltransferase (HPRT)¹ (4). Thus, we have been able to select mutants from WI-L2 which are virtually completely deficient in adenosine kinase (AK) and adenine phosphoribosyltransferase (APRT). The gene for APRT has been mapped to human autosomal chromosome 16 (5) and that for AK tentatively to chromosome 10. Such mutants selected in vitro are essentially isogenic with their parental line and, in the case of the mutants to be described, have identical rates of growth.