Chinese hamster cells mutant for hypoxanthine-guanine phosphoribosyltransferase (HPRT) locus. V. Complementation analysis of ts mutants

Four clones temperature-sensitive for HPRT were employed in hybridological analysis, which led to an increase in complementation frequency by a factor of ∼ 5. The probability of complementation for the HPRT locus was found to be quite high: 14 of the 45 mutants tested in hybridization were capable of complementation, including three ts mutants. Analysis of the frequency with which the mutants participated in complementation showed a clear dependence on the selective conditions under which they were obtained: clones isolated in medium containing 8-azaguanine most frequently exhibited complementation. Use of the mutants with the new phenotype for hybridization revealed an additional four complementation groups, three of which formed temperature-sensitive clones. Biochemical studies showed that hybrid forms of the enzyme HPRT were present in all the hybrids investigated. The intragenic character of complementation was thus confirmed. The functional map of the HPRT locus is presently composed of nine groups, including a group of noncomplementing mutants