Expression of a beta-galactosidase gene containing the ribosomal protein 51 intron is sensitive to the rna2 mutation of yeast.

The temperature-sensitive mutation rna2 causes the accumulation of higher molecular weight transcripts from the ribosomal protein 51 (rp51) gene of yeast and many other yeast ribosomal protein genes. We have determined the DNA sequence of the rp51 gene, confirming that it contains an intron and that the higher molecular weight transcript is an intron-containing precursor RNA. These data and other experiments suggest that the rna2 mutation affects mRNA processing (splicing) and that the presence of an intron is sufficient to render expression of a gene sensitive to the rna2 mutation. To test these hypotheses, we have inserted the rp51 intron into the coding region of a hybrid Escherichia coli beta-galactosidase gene, thereby interrupting the open reading frame subsequent to the initiating methionine codon. Despite the presence of the intron, the beta-galactosidase gene is expressed in yeast. Thus, the rp51 intron is properly excised from the normally intronless gene. The presence of the rp51 intron causes the beta-galactosidase activity to be sensitive to the rna2 mutation, consistent with the notion that this mutation affects gene expression at the level of splicing. The experiments suggest that an intron-containing beta-galactosidase gene can be used in a general way to study mRNA splicing.