Male C57BL/6 mice were treated with ENU and subsequent generations screened for reduced expression of H2-A (mouse MHC-II) protein on the surface of peripheral blood lymphocytes (PBLs), resulting in the identification of this allele. The point mutation of the conserved A at position 408 of intron 2 branch site to T leads to aberrant splicing, resulting in reduced expression of H-2A mRNA and protein to around 12% of wildtype levels. In addition to reduced level of wildtype H-2A mRNA, the A-to-T branch site point mutation causes the formation of two aberrant mRNAs species, one of which is spliced using a cryptic splice acceptor in intron 2, while the other results from intron 2 read-through. Both of these aberrant mRNA species encode non-functional premature terminated H-2A protein. (J:244717)