HUMAN-COMPLEMENT PROTEIN C2 - ALTERNATIVE SPLICING GENERATES TEMPLATES FOR SECRETED AND INTRACELLULAR C2 PROTEINS

Alternative splicing of the primary transcript for human complement pr otein C2 generates templates for translation of a secreted (C2 long) p rotein and an intracellular (C2 short) form in liver, bronchoalveolar macrophages, and fibroblasts. The approximate ratio of C2 long to C2 s hort mRNA is 2:1. The C2 short mRNA does not contain the 396-base pair encompassed by exons 2 and 3 of the full-length C2 long and thus lack s codons for the 5 carboxyl-terminal residues of the signal peptide, S ynthesis of C2 in cells transfected with full-length INA corresponding to each of the transcripts show that C2 long is secreted within a hal f-time of approximately 1 h and that C2 short is not secreted. Cell-fr ee biosynthesis in the presence of microsomes demonstrate that this in tracellular C2 protein (70 kDa) is apparently capable of traversing th e membrane of the endoplasmic reticulum. Though the function of the in tracellular C2 protein is unknown, it is abundant in all cell types th at express the C2 gene.