Ultrastructural Localization of Tritiated Histidine in Down Feathers of the Chick

During the differentiation of cells in developing down feathers of the chick embryo, keratin and associated proteins are synthesized. Previous studies indicated that a histidine-rich protein with a different amino acid composition but similar molecular weight and localization of feather keratin is produced in forming feathers. The precise localization of the histidine-rich protein, either in feather barb and barbule cells and/or in supportive...