Analysis of the yeast genome: identification of new non-coding and small ORF-containing RNAs

The genome sequences from increasing numbers of organisms allow for rapid and organized examination of gene expression. Yet current computational-based paradigms for gene recognition are limited and likely to miss genes expressing non-coding RNAs or mRNAs with small open reading frames (ORFs). We have utilized two strategies to determine if there are additional transcripts in the yeast Saccharomyces cerevisiae that were not identified in previous analyses of the genome. In one approach, we identified strong consensus polymerase III promoters based on sequence, and determined experimentally if these promoters drive the expression of an RNA polymerase III transcript. This approach led to the identification of a new, non-essential 170 nt non-coding RNA. An alternative strategy analyzed RNA expression from large sequence gaps>2 kb between predicted ORFs. Fifteen unique RNA transcripts ranging in size from 161 to 1200 nt were identified from a total of 59 sequence gaps. Several of these RNAs contain unusually small potential ORFs, while one is clearly non-coding and appears to be a small nucleolar RNA. These results suggest that there are likely to be additional previously unidentified non-coding RNAs in yeast, and that new paradigms for gene recognition will be required to identify all expressed genes from an organism.