PROTEIN-SYNTHESIS DURING FETAL DEVELOPMENT OF MOUSE EPIDERMIS .2. BIOSYNTHESIS OF HISTIDINE-RICH AND CYSTINE-RICH PROTEINS INVITRO AND INVIVO

The biosynthesis of specific epidermal proteins at different stages in the development of fetal mouse epidermis has been investigated. Skin pieces from 16- to 17-day or 18- to 19-day fetal mice were incubatedin vitro with the individual amino acids [3H]histidine or [35S]cystine, or with a mixture of14C-labelled amino acids. Labelled proteins were extracted, then separated by SDS-polyacrylamide gel electrophoresis, and the newly synthesised proteins were identified by gel fluorography. The results demonstrated that several histidine-rich proteins (HRP) in the MW range 70,000-120,000 are very rapidly synthesisedin vitro. At least one of these proteins was actively synthesised in epidermis from 16- to 17-day mice, i.e., at a stage which precedes the appearance of histidine-rich keratohyalin granules. Noin vitro incorporation was observed at any stage into the major HRP constituent of mouse epidermis (MW 27,000; Balmainet al., 1977), although this protein was strongly labelledin vivo. Incorporation of [35S]cystinein vitro andin vivo indicated that a protein(s) of MW 66,000 is very rich in this amino acid. © 1979 Academic Press, Inc. All rights reserved.