Mouse immunoglobulin subclasses: cyanogen bromide fragments and partial sequence of a gamma1 chain.

The purification and characterisation of all the cyanogen bromide fragments of MOPC 21 heavy (gamma1) chain is described. The ten BrCN fragments account for the whole chain. Four of these fragments have been used to establish the sequence of the C-terminal stretch (138 residues) that includes the entire CH3 and a part of the CH2 homology regions. A comparison of this sequence with homologous sequences is presented. Mouse gamma1 and gamma2 proteins differ much more than the gamma subclasses in humans and in other species. The comparison further suggests that the four human gamma subclasses and mouse gamma1 have a common ancestor which differs from the mouse gamma2 ancestor. Unlike other subclasses, mouse gamma1 and gamma2 genes have diverged before speciation.