Intracellular processing of the Sendai virus C′ protein leads to the generation of a Y protein module: Structure–functional implications

The Sendai virus “ C-proteins” (C′, C, Y1 and Y2) are a nested set of non-structural proteins. The shorter Y proteins arise in vivo both by de novo translation initiation and by proteolytic processing of C′. In this paper, we demonstrate that C′ but not C (differing only by 11 N-terminal amino acid) serves as an efficient substrate for intracellular processing. However, processing can be mimicked in vitro by the addition of endopeptidases. Under conditions of limited proteolysis we observed that in a fraction of the C′ protein the Y region exists as a proteinase resistant core. This core was conserved in the C protein. We propose that C′ functions as a Pro-protein delivering the Y module to a specific intracellular location.