Allotypes of murine factor B controlled by a locus within the S region of the H-2 complex

Abstract

Bf protein was directly precipitated from a mixture of EDTA-plasma from 13 different, inbred strains and rabbit IgG anti-mouse Bf, and was isolated by SDS-PAGE. The gel pieces containing Bf protein were digested by trypsin after labeling with 125I-Na, and then peptides of Bf protein with each mouse strain were compared by two-dimensional peptide mapping. The results for the peptide patterns with the standard B10 congenic strains (all of which Bf phenotypes had been already designated as Bf.1 because of the identical isoelectric point values) revealed two distinct peptide patterns. The peptide pattern of Bf protein appeared to be identical in each of the inbred strains, but only one of the 36 spots in the fingerprint observed either with B10 or B10.BR (designated tentatively as Bf.1 (b.k.) ) was not detected in that from B10.D2 and B10.S (designated tentatively as Bf.1 (d.s.) ). The results of peptide mapping with intra-H-2 recombinant inbred strains show that this structural variant was mapped to the S region, which is direct evidence that allotypes of murine Bf are encoded by a structural gene within the MHC.