Localization of a gene which complements branched-chain amino acid transaminase deficiency to the short arm of human chromosome 12.

A human X Chinese hamster somatic cell hybrid (J1) containing only one human chromosome (number 11) does not express branched-chain amino acid transaminase and, therefore, cannot grow if the branched-alpha-keto acids are substituted for the branched-chain amino acids in the growth medium. J1 cells, which are glycine auxotrophs (Gly-A), were fused with normal human lymphocytes and the resulting hybrids selectively isolated in glycine-free medium. A total of 16 primary and 46 secondary clones were analyzed for isozymic and nutritional markers. Cytogenetic analysis with chromosome banding was also performed on selected hybrid clones. The results provide evidence that branched-chain amino acid transaminase is syntenic with lactic dehydrogenase B and is located on the short arm of human chromosome 12.