The relationship between coding sequences and function in some heme binding proteins.

It is known that globin genes contain three exons with the middle exon coding for a four-helical supersecondary structure responsible for heme binding. Since this portion of the globin peptide chain can be structurally superimposed onto the cytochrome c and cytochrome b5 chains (Argos and Rossmann 1979), it can be inferred that the cytochrome c gene will contain only one coding sequence while the cytochrome b5 gene will be composed of three exons as found in the globin gene.