In an earlier paper, we presented evidence that two independent mutants of the bg series, B6-H-2bm5 (bm5) and B6-H-2bm16 (bm16) carry identical mutations such that tyrosine at residue number 116 of the H-2Kb molecule from the parent strain C57BL/6Kh is replaced by a phenylalanine in each of the two mutant molecules. In this paper, we demonstrate, using similar techniques, that the independent bg series mutants B6-H-2bm6 (bm6), B6.C-H-2bm7 (bm7), and B6.C-H-2bm9 (bm9), which share biological properties with bm5 and bm16, can be grouped together because they share two identical mutations, one of which is common to bm5 and bm16, a Tyr to Phe interchange at residue number 116. In addition, a second mutation is at residue number 121, where a Cys in the H-2K molecule from 136 is substituted with an Arg in the mutant. Since all of the bg series mutants arose independently and share biological and biochemical characteristics, it is anticipated that study of these mutants could lead to some understanding of the high mutation rate in the Kb molecule.
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