Signals controlling alternative splicing of major histocompatibility complex H-2 class I pre-mRNA.

The use of alternative splice acceptor sites during the removal of intron 7 in pre-mRNA splicing produces two forms of H-2Kb protein: the predominant form, derived from a transcript that has spliced at the upstream splice acceptor site for exon 8 (long exon 8), and a Kb molecule derived from a transcript that has spliced at the downstream acceptor site for exon 8 (short exon 8). We have identified a potential lariat branch point adenosine for the upstream acceptor splice site. This adenosine is found 28 bp from the splice junction and is contained in the sequence AGTGATGG. D-region genes, which use only the downstream splice site, have the sequence AGTGGTGG. We have used in vitro mutagenesis to change this A of the H-2Kb gene to G and have made the reciprocal change in H-2Dd. Elimination of this adenosine in H-2Kb alters the pattern of pre-mRNA splicing and results in a predominance of the Kb molecules with short exon 8 encoded sequences. However, the addition of an adenosine in H-2Dd is not sufficient to direct splicing to the upstream site.