Absence of demonstrable linkage of human genes for enzymes of the purine and pyrimidine salvage pathways in human-mouse somatic cell hybrids

A number of different reduced human-mouse hybrids have been analyzed for the presence of human enzymes of the purine and pyrimidine salvage pathways. Homologous mouse and human enzymes were characterized by isoelectric fractionation or gel electrophoresis, and the species of origin of the enzyme in hybrid clones was determined. Hybrids selected for one of the human enzymes, thymidine kinase, adenine phosphoribosyltransferase, or hypoxanthine phosphoribosyltransferase, were each found to contain the selected enzyme but not the other two. Neither human adenosine kinase nor human deoxycytidine (cytidine) deaminase was present in any of the hybrid clones. A human 5′-nucleotidase was present in two hybrid clones containing human hypoxanthine phosphoribosyltransferase, but the genes for the two enzymes are not linked. The genes for the purine and pyrimidine salvage enzymes appear to be dispersed in the human genome.