NH2-TERMINAL SEQUENCE OF THE CHICK PRO-ALPHA-1(I) CHAIN SYNTHESIZED IN THE RETICULOCYTE LYSATE SYSTEM - EVIDENCE FOR A TRANSIENT HYDROPHOBIC LEADER SEQUENCE

Abstract

Translation of chick procollagen mRNA [from cranial bone] in a reticulocyte lysate system yields a larger pro.alpha.1(I) chain than is observed in vivo. The NH2-terminal sequence of this putative precursor was determined by automated radiosequencing. The sequence closely resembles the transient hydrophobic leader (signal) sequences observed on most secreted proteins. When synthesized in the presence of microsomal membranes from dog pancreas, which contain signal peptidase activity, pro.alpha. chains with the electrophoretic mobility of underhydroxylated procollagen polypeptides synthesized in vivo are produced. Estimates of the MW of the NH2-terminal extension of the precursor suggest that the leader sequence may be longer than those commonly found in precursors of secreted proteins.