Molecular cloning, genomic organization, and mapping of PRKAG2, a heart abundant gamma2 subunit of 5'-AMP-activated protein kinase, to human chromosome 7q36.

5'-AMP-activated protein kinase (AMPK) acts as a major regulator of cellular ATP levels and protects cells against stresses that cause ATP depletion. AMPK is a protein heterotrimer composed of a catalytic alpha subunit and two regulatory subunits, beta and gamma. In the present study, a homologue of the AMPK gamma1-subunit cDNA with an open reading frame encoding 328 amino acids was identified. The putative protein sequence is about 76% identical to the 331-amino-acid gamma1 subunit and also has four consecutive cystathionine-beta-synthase (CBS) domains, a characteristic structure of AMPK gamma subunits from various species. This cDNA (tentatively termed PRKAG2-b) is identical to a recently reported cDNA (tentatively termed PRKAG2-a) of human AMPK gamma subunits except in their 5'-end regions, suggesting that these two cDNAs are two different transcripts of the same gene. To determine the expression pattern of the gene, two probes, one from the 3'-UTR of PRKAG2-b and the other from the 5'- unique region of PRKAG2-a, were used to hybridize MTN membranes. Three transcripts (3.8, 3.0, and 2.4 kb) were observed when the first probe was used, whereas only 3.8- and 3.0-kb transcripts were seen when the second probe was used. Thus, the PRKAG2-b corresponded to the 2.4-kb transcript, which is ubiquitously expressed except in liver and thymus. The highest level was detected in heart, while abundant expression also existed in placenta and testis. The expression pattern of PRKAG2-b is completely different from those of PRKAG2-a and PRKAG1, whose expression patterns were also determined in the current study. The PRKAG2 gene was located to human chromosome 7q36 between markers D7S2439 and D7S2462 by radiation hybrid mapping. The genomic organization of PRKAG2-b was identified by comparing its cDNA sequence with two genomic sequences AC006358 and AC006966, which showed that PRKAG2-b spanned an approximately 80-kb region and was composed of 12 exons.