Multiple amino acid substitutions between murine gamma 2a heavy chain Fc regions of Ig1a and Ig1b allotypic forms.

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Abstract
The complete amino acid sequence of the murine .gamma.2a H chain CBPC-101 Fc region of allotype Ig1b was determined by automated and manual Edman degradation procedures. Both chemical and enzymatic cleavages were used to obtain peptides which were purified by gel filtration followed by high-pressure liquid chromatography. The sequence was in good agreement with that predicted from the nucleotide sequence of a .gamma.2a gene of allotype Ig1b except for 2 positions. Comparison with published data on MOPC-173 .gamma.2a H chain of allotype Ig1a revealed 8 amino acid substitutions in the CH2 domain (7% differences) and 28 substitutions (27%) in the CH3 domain. Many of the observed interchanges occur at positions at which murine H chains of other classes also differ from the .gamma.2a chains. The divergence of the .gamma.2a Ig1a gene found in BALB/c mice and of the .gamma.2a Ig1b gene found in CB 20 mice must have occurred long ago; the CH2 domain was probably much more conserved than the CH3 domain.