Inhibition of protein synthesis in vitro by procollagen-derived fragments is associated with changes in protein phosphorylation.

The NH2-terminal extension fragment (Col 1) of the pro alpha 1(I) procollagen chain selectively inhibits the translation of procollagen mRNA in a reticulocyte lysate system, whereas the reduced and alkylated fragment (AE-Col 1) and its proteolytically derived peptides inhibit the translation of all mRNAs (Hörlein, D., McPherson, J., Goh, S. H., and Bornstein, P. (1981) Proc. Natl. Acad. Sci. U.S.A. 78, 6163-6167). The latter inhibitory function, which occurs at the level of polypeptide chain initiation, has now been shown to be associated with an increase in phosphorylation of an Mr = 94,000 protein. The time span required for observation of changes in phosphorylation and in inhibition of protein synthesis is similar. Since AE-Col 1 can serve as a substrate for casein kinase II, we suggest that phosphorylation of AE-Col 1 and its derivatives may be required for their activity.