Genetic defect in biosynthesis of the precursor form of the fourth component of complement.

Under cell-free conditions, liver polysomes from guinea pigs genetically deficient in the fourth component of complement (C4) did not synthesize pro-C4 (the precursor of C4), but did synthesize nascent C4 polypeptides which remained polysome bound. The defect was specific for pro-C4 synthesis since the amounts of total protein and albumin synthesis and release from C4-deficient polysomes were similar to that in normal guinea pig liver polysomes.