Structural and transcriptional analysis of a chicken myosin heavy chain gene subset.

Recently we have isolated a large number of chicken myosin or myosin-like heavy chain genes. Seven of these genes were placed into a subset based upon their hybridization patterns. In the present study, the sequence of the 5' end of one of the myosin heavy chain (MHC) genes, N127, was determined and compared with the 5' end sequences of the other six MHC genes in the subset. The comparison revealed that the three exons encoding the amino termini of the protein are highly conserved. The sequence analysis shows that a localized correction event occurred in and around a domain of the nucleotide-binding site, as the exon encoding this site and the preceding intron are very highly conserved among the seven genes. The sequence of the promoter and 5'-untranslated region of N127 is presented. The analogous regions for N124 and N125 have now been sequenced and are also presented. As is the case for all the other known MHC genes, the 5'-untranslated regions are split by large introns. The promoter and 5'-untranslated regions are compared with two previously characterized chicken MHC genes (N116 and N118) to determine the sequence similarities and differences that might underlie the differential expression of the family's members. To confirm and extend previously published results of the expression of these genes, transcript-specific probes generated from the 5' region of six of the seven genes were used to determine in which muscle(s) the corresponding mRNAs were present. The data show that despite the very close structural homologies, each of the genes for which a unique probe could be prepared exhibits a unique pattern of expression.