[Chinese hamster cells mutant for the hypoxanthine-guanine phosphoribosyltransferase locus. II. Characteristics of the hybrids revealing intragenic complementation].

After polyethylene glycol treatment of GPRT- mutant cells, 12 clones were isolated on the ATG medium showing intragenic complementation. Karyological analysis confirmed the hybrid nature of the clones isolated. The GPRT activity in the hybrid clones, as assessed in vitro, exceeded the sum of parental activities. In vivo incorporation of 14C-hypoxanthine showed the GPRT activity in the hybrids to be an order of magnitude higher than in the mutant parental cells. Moreover, the GPRT activity in the hybrid clones was found to increase considerably during cultivation on the ATG medium; hence, their ability to multiply on this selective medium. All hybrid cells surviving and multiplying on the ATG medium were shown to maintain a high enough resistance to 8-AG, 6-MP and, to somewhat less extent, to 6-TG. The frequency of complementation was determined for the cells of mutant clones selected on media with different purine base analogues. The complementation map for the GPRT locus was constructed and proved to be linear. Five groups of complementation were specified.