Soluble and membrane-bound forms of cytochrome b₅ are the products of a single gene in chicken

In order to determine the relationship of the soluble cytochrome b₅ found in erythrocytes to the membrane-bound form found in other tissues, a cDNA clone encoding cytochrome b₅ in chicken erythrocytes was isolated by using mixed oligonucleotides based on a partial amino acid sequence of the protein. Complete nucleotide sequence identity between the erythrocyte cDNA and the sequence of a cDNA clone of the liver protein suggests that they are transcribed from the same gene. The isolation and structural analysis of genomic clones was also consistent with the presence of only one cytochrome b₅ gene in chicken. These results suggest that the formation of soluble erythrocyte cytochrome b₅ occurs by proteolytic processing of the membrane-bound form. Thus, previous reports indicating that the carboxyl terminal amino acid residue of the erythrocyte form differs from the corresponding residue of the membrane-bound form may suggest the existence of a novel post-translational modification.