BIOCHEMICAL AND GENETIC PROPERTIES OF HPRT _{CAPE TOWN}: 66

Abstract

HPRT_{Cape Town} possesses the unique kinetic property in erythrocyte extracts of substrate inhibition by its purine substrates (1). In order to determine whether these properties reflect a mutation in the HPRT gene or in a gene for a putative regulatory polypeptide, the kinetic properties of HPRT from the proband's daughter, as well as growth properties of transformed lymphoblasts, were studied. Lymphoblasts from the daughter showed similar ¹⁴C hypoxanthine uptake (relative to ³H thymidine) in the proband's cells, and similar growth properties in selective media. However, the kinetics of HPRT in her erythrocyte extracts were intermediate between normal and proband erythrocytes indicating that she was heterozygous for the defect and therefore that the defect in HPRT_{Cape Town} is in the gene for HPRT itself. DNA from the proband's and his daughter's cells were analysed by restriction endonuclease analysis and mRNA by S1 nuclease analysis using a cloned human HPRT probe.

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