A New Reduced Human-Mouse Somatic Cell Hybrid Containing the Human Gene for Adenine Phosphoribosyltransferase

A system that selects for the gene directing synthesis of the enzyme adenine phosphoribosyltransferase (APRT) uses the antibiotic alanosine to prevent endogenous synthesis of adenylic acid. With the aid of this system, a new series of human-mouse hybrids has been prepared between wild type human diploid fibroblasts and an enzyme-deficient mouse line. Survival of the hybrids depended upon the presence of the APRT, which was shown to have the isoelectric pH characteristic of the human enzyme and not that of the mouse. Reduced hybrids containing the enzyme lacked all human biarmed chromosomes, so that unless a rearrangement had occurred, the aprt gene must be located on an acrocentric chromosome. The hybrid cells became APRT(-) with a frequency of 2 x 10(-3), probably by loss of the human aprt chromosome. The APRT(-) progeny could be obtained selectively by growth in medium containing fluoroadenine.