The minor U12-dependent class of eukaryotic nuclear
pre-mRNA introns is spliced by a distinct spliceosomal
mechanism that requires the function of U11, U12, U5, U4atac,
and U6atac snRNAs. Previous work has shown that U11 snRNA
plays a role similar to U1 snRNA in the major class spliceosome
by base pairing to the conserved 5′ splice site sequence.
Here we show that U6atac snRNA also base pairs to the 5′
splice site in a manner analogous to that of U6 snRNA in
the major class spliceosome. We show that splicing defective
mutants of the 5′ splice site can be activated for
splicing in vivo by the coexpression of compensatory U6atac
snRNA mutants. In some cases, maximal restoration of splicing
required the coexpression of compensatory U11 snRNA mutants.
The allelic specificity of mutant phenotype suppression
is consistent with Watson–Crick base pairing between
the pre-mRNA and the snRNAs. These results provide support
for a model of the RNA–RNA interactions at the core
of the U12-dependent spliceosome that is strikingly similar
to that of the major class U2-dependent spliceosome.