Fine assignment of beta-hexosaminidase A alpha-subunit on 15q23-q24 by high resolution in situ hybridization.

Tay-Sachs disease results from mutation in the gene encoding beta-hexosaminidase A alpha-subunit. Although some reports have suggested the locus on 15q, we tried to determine the finer gene locus using high resolution in situ hybridization. cDNA probe, p beta H alpha-5, containing the full-length sequence for the enzyme subunit, was 3H-labeled within 1-4 x 10(7) cpm/micrograms of cDNA by nick-translation. After molecular hybridization and autoradiography, prometaphases were G-banded by Hoechst 33258, UV-exposure and Giemsa. A total of 227 silver grains on chromosomes within 115 prometaphase spreads were analyzed. The region 15q23-q24 had 27 grains, corresponding to 11.9% of the total grains and to 77.1% of the grains on chromosome 15. 20.9% of prometaphases were observed with a grain at 15q23-q24. According to several previous reports, the shortest region of overlap (SRO) of the locus has been 15q22-q25.1. Here we have assigned the gene locus to the narrower region 15q23-q24 by high-resolution in situ hybridization, which is one of the most powerful strategy for the completion of human gene map.