Qa-region class I gene expression: identification of a second class I gene, Q9, encoding a Qa-2 polypeptide.

A feature of the expression of the tissue-specific class I antigen Qa-2 is the quantitative variation among mouse strains. Recently, the class I gene Q7 has been shown to encode a protein product that is biochemically indistinguishable from the lymphocyte-bound Qa-2 molecule. Utilizing gene transfection, we have identified a second Qa-2 subregion class I gene (Q9), in H-2b mice, which encodes a polypeptide biochemically similar to the Q7 and the Qa-2 polypeptides. Furthermore, we have observed that cell lines transfected with the allelic forms of the Q7 gene from C57BL/10 (Qa-2hi) or BALB/C (Qa-2low) display quantitative differences in cell-surface expression. Based on these studies, we suggest that gene dosage and allele-specific variation in cell-surface expression contribute to the strain-specific variation in the levels of Qa-2 antigen expression.