ABSTRACT
The enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT) catalyzes the phosphoribosylation of the purine bases hypoxanthine and guanine to form inosine and guanosine monophosphate. The HPRT gene is, in addition, of medical interest, since HPRT deficiency results in the severe neurological disorder Lesch-Nyhan syndrome. Revertants of RJK526 showed up to fivefold amplification, with no evidence of chromosomal alteration, and twofold amplification occurred in the RJK531 revertants. One group of revertants contained normal levels of HPRT protein with the same heat stability, electrophoretic mobility, and kinetic properties as the protein from wild-type cells. Revertants also fell into two groups, with one group containing a normal HPRT protein and the second group overproducing a mutant protein as a consequence of 20-fold gene amplification. The other HPRT-deficient mutants that have given rise to revertants with gene amplification are all derivatives of the Chinese hamster lung cell line, V79.
