In vitro studies on the synthesis of guinea pig hair keratin proteins

Abstract

1. The “high-sulphur” keratin proteins that comprise the matrix moiety of hair have been synthesized in a cell-free protein synthesis system from guinea pig hair follicle tissue. 2. These findings, in conjunction with the previous studies on the cell-free synthesis of the “low-sulphur” keratin proteins, demonstrate that the keratin proteins are synthesized in vivo by the classical ribosomal-dependent mechanism. This conclusion makes unlikely the suggestions by other workers that a non-ribosomal-dependent mechanism could be responsible for the basic synthesis of the keratin proteins. 3. Estimates were made of the amount of de novo synthesis of the low-sulphur proteins and the high-sulphur proteins. It was found that 14–18 % of all low-sulphur proteins synthesised in vitro were synthesised de novo and only about 2 % for the high-sulphur proteins. It is proposed that the findings could reflect differences in the rates of translation of the mRNAs for the low-sulphur and high-sulphur proteins. Since these proteins contain high and variable amounts of S- carboxymethylcysteine , then the level of cysteinyl-tRNA may limit the rates of translation in vitro. This conclusion is discussed in relation to observations on the synthesis of the keratin proteins in vivo.