title: The keratin chains of avian scale tissue. Sequence heterogeneity and the number of scale keratin genes.
abstract: The three major proteins of chick scale keratin were isolated as their S-carboxymethylated derivatives and shown to be similar or identical in molecular weight by gel filtration but to be distinct by amino acid analysis and gel electrophoresis. The major amino-terminal sequence of scale keratin chains was determined and shown to be highly homologous to the corresponding region of feather keratin chains. The carboxyl-terminal peptides of the three scale keratin fractions differed in sequence but were all homologous to the carboxyl-terminal segment of feather keratin chains. The pronounced concentration of cysteine residues at the amino-terminal and carboxyl-terminal segments suggested a similar role for these regions in both scale and feather keratin chains, namely to provide a disulphide-linked matrix to maintain the organisation of fibrils which arise from the internal hydrophobic segments of both types of chain. Analysis of a large hydrophobic segment from each of the three isolated protein fractions revealed that each was composed largely of repeating tripeptide units of the type Gly-Gly-X (where X = Phe, Leu or Tyr). At a few positions in each hydrophobic peptide, microheterogeneity was apparent in the sequences indicating that each isolated protein fraction was composed of at least three different chains each encoded by a different gene. A minimum of nine keratin genes are therefore expressed in scale tissue.
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001717:Birds; D002645:Chickens; D005796:Genes; D007633:Keratins / Q000096:biosynthesis; D046911:Macromolecular Substances; D008970:Molecular Weight; D010446:Peptide Fragments / Q000032:analysis; D012867:Skin / Q000378:metabolism*; D013045:Species Specificity; D014357:Trypsin
chemical_list: D000596:Amino Acids; D046911:Macromolecular Substances; D010446:Peptide Fragments; D007633:Keratins; D014357:Trypsin