In vitro synthesis of a regulator of mammalian gene expression.

Peritoneal cells isolated from guinea pigs homozygous for a deficiency of the fourth component of complement (C4), produce in vitro a factor that induces the synthesis and secretion of functionally active human C4 by a human cell. This factor appeared to switch on production of C4 in the responsive cell without affecting total protein synthesis. The regulator factor is not species specific, inasmuch as guinea pig regulator affected a corresponding human gene function. Both synthesis of the factor and the response to it were inhibited by actinomycin D. The amount of regulator recovered from genetically deficient cells was about 5-10 times that recovered from normal guinea pig cells.