Use of a high-efficiency expression vector to isolate cDNA clones for factor H and map their positions within the molecule.

A human liver cDNA library, cloned in a novel high-efficiency bacterial expression vector (PEX), was screened with an affinity-purified antibody to human factor H. Four distinct cDNA clones, H-2, H-40, H-46 and H-49, were identified. Of these, H-2 also reacted with two monoclonal antibodies to H, MAH-4 and OX-24, which were previously shown to recognize the 38,000 N-terminal tryptic fragment of H, carrying the binding site for C3b. By using polyclonal antibodies specific for the domains in H coded for by these cDNA-clones, it could be established that H-2 codes only for the 38,000 N-terminal tryptic fragment of H, whereas H-40, H-46 and H-49 are derived from the 142,000 C-terminal fragment of H. By subcloning H-2 the epitope for OX-24 could be localized as being coded near the central Sma-site of H-2.