THE GENE ENCODING RAT PHOSPHOGLYCERATE MUTASE SUBUNIT-M - CLONING ANDPROMOTER ANALYSIS IN SKELETAL-MUSCLE CELLS

The expression of the gene encoding the muscle-specific (M)-subunit of phosphoglycerate mutase (PGAM-M) is restricted to adult skeletal and cardiac muscle. In order to study its expression in muscle, the rat PG AM-M gene has been isolated and sequenced. Rat PGAM-M spans about 2.2 kb and is composed of three exons: 442, 181 and 186-bp long, and two i ntrons of 97 bp and 1.3 kb. The analysis of the 5'-flanking region rev eals a promoter which contains multiple DNA regulatory elements and co nstitutes an ideal model to study muscle gene transcriptional regulati on. Thus, the elements responsible for rat PGAM-M muscle-specific expr ession have been identified by transient transfection in chicken embry o primary cultures, using chimeric constructs of the rat promoter link ed to a cat reporter gene. Here, we report that in spite of the abunda nce of E-box motifs in the rat PGAM-M promoter, known for their involv ement in muscle gene expression, two DNA elements regulate the muscle- specific transcription of rat PGAM-M: an A/T motif, the putative MEF-2 -binding site (myocyte-specific enhancer-binding factor 2), and a prox imal 27-bp element which is conserved between the rat and human genes. These two elements define a small promoter (170 bp) sufficient to sup port potent and skeletal-muscle-specific expression. The conserved 27- bp region constitutes a transcriptional regulatory element able to con fer muscle-specific expression when located upstream from a heterologo us TATA box.