Abstract
A spontaneous mutation of H-2Kb, Kbm29, was discovered among the progeny of F1 hybrid parents. Unlike other characterized spontaneous class I variants, this mutant was detected with the use of antibody, rather than tissue grafting. Although Kbm29 is serologically indistinguishable from the previously described mutant molecule Kbm3, it is identical to the parental Kb by skin grafting and CTL assays. A full length cDNA of Kbm29 was amplified by polymerase chain reaction with locus-specific primers, cloned, and sequenced. Two nucleotides were found to be mutated, resulting in a single amino acid change (Lys----Ala) at amino acid 89 of the mature glycoprotein. This is consistent with the observed serologic changes, as the same amino acid substitution is responsible for the serologic profile of Kbm3. The occurrence of a mutation which is not detectable by the methods normally used to screen for H-2 mutants provides evidence that the high spontaneous rate of structural mutation described for the Kb molecule is underestimated.