Identification of a genomic locus containing three slow myosin heavy chain genes in the chicken

Two unique cDNA clones containing chicken slow myosin heavy chain (MyHC) inserts have been isolated from an expression library. Immunochemical analyses of the expressed proteins using different slow MyHC specific monoclonal antibodies were consistent with the two clones encoding slow MyHC 1 (SM1) and slow MyHC 2 (SM2) protein sequences. Northern blot analyses showed that the clones hybridized with 6-kb mRNAs that are differentially expressed in developing and adult slow muscles, further supporting the conclusion that these two clones represent SMI and SM2 cDNAs. Sequence analyses show that both clones encode the highly conserved fight meromyosin portion of the sarcomeric myosin rad and are 78-81% homologous to a mammalian slow/cardiac beta-MyHC cDNA. Hybridization using PCR generated probes specific for SMI and SM2 sequences demonstrated that the genes encoding these two slow MyHCs colocalized to an XO-kb BssHII genomic fragment, We further show that a probe specific to a third slow MyHC gene also hybridized with the same 80-kb genomic fragment. We conclude that in the chicken genome there is a slow MyHC locus containing at least three distinct slow MyHC genes. (C) 1997 Elsevier Science B.V.