Carboxy-terminal-extended variant of the human fibrinogen alpha subunit: a novel exon conferring marked homology to beta and gamma subunits.
Fu Y., Weissbach L., Plant P.W., Oddoux C., Cao Y., Liang T.J., Roy S.N., Redman C.M., Grieninger G.
Similarities between the N-terminal regions of the three subunits of the clotting protein fibrinogen--(alpha beta gamma)2--suggest that they evolved from a common progenitor. However, to date no human alpha chain has been found with the strong C-terminal homology shared by the beta and gamma chains. Here we examine the natural product of a novel fibrinogen alpha chain transcript bearing a separate open reading frame that supplies the missing C-terminal homology to the other chains. Additional splicing leads to the use of this extra sequence as a sixth exon elongating the alpha chain by 35%. Since the extended alpha chain (alpha E) is assembled into fibrinogen molecules and its synthesis is enhanced by interleukin-6, it suggests participation in both the acute phase response and normal physiology.