The baboon beta-myosin heavy-chain gene: construction and characterization of cDNA clones and gene expression in cardiac tissues.

We have constructed a cDNA library from baboon ventricle and have used a rabbit beta-myosin heavy chain (beta-MHC) cDNA probe to isolate cross-hybridizing clones. The nucleotide sequence of one such clone, lambda BMHC beta 14, contains a portion of the coding region of the light meromyosin (LMM) region and the 3'-untranslated region of the baboon ventricular MHC. This cDNA clone is identified as containing beta-MHC sequences on the basis of similarity with the 3'-untranslated regions of beta-MHC genes from man (96% homologous) and rat (71% homologous), and dissimilarity with the 3'-untranslated region of the rat alpha-MHC gene (25% homologous). Alignment and comparison of the baboon cDNA nucleotide sequence with a human cDNA sequence reveal two amino acid substitutions in the LMM region that cause differences in their hydrophilicity profiles. These differences may alter MHC functions such as filament assembly. We have used baboon beta-MHC cDNA clones to construct probes for S1 nuclease protection studies to detect and to distinguish cardiac MHC gene transcripts in baboon ventricle, atrium, and diaphragm. As in human tissues, beta-MHC gene transcripts are detected in RNA from baboon ventricle and diaphragm. In baboon atrium, we detect beta-MHC gene transcripts as well as transcripts that may represent expression of the alpha-MHC gene. This study represents the first examination of cardiac MHC genes and gene expression in tissues from a large mammal that is closely related to man.