| Popis: |
The yeast, Saccharomyces cerevisiae, has previously been shown to have a transcriptome comprising over 6,000 protein coding genes, as well as over 900 noncoding RNAs (ncRNAs). This work focuses on the regulation of the gene IME4, which is normally expressed only in a/α diploid cells. In haploid cells, an ncRNA, which I have termed Regulator of Meiosis 2, (RME2) is expressed from the antisense strand of IME4.RME2 has a direct role in the haploid-specific repression of IME4. I have shown that RME2 represents a novel class of cis-acting non-coding RNA regulators, as it does not regulate in a trans-acting mechanism like microRNA. Furthermore, RME2 represses IME4 transcription in a promoter-independent mechanism, as transcription factor binding at the IME4 promoter is not perturbed. Regulation by IME4 does appear to require transcription across specific sequences within the IME4 ORF itself; in absence of the required sequences, IME4 and RME2 are co-expressed. In addition to IME4, this work details another meiotic gene, ZIP2, which was found to have a similar regulatory antisense transcript, RME3. Like RME2, RME3 represses in a cis- acting mechanism. To determine if other genes are regulated in a manner similar to IME4 and ZIP2, strand-specific RNA-sequence analysis was used to compare the antisense transcriptomesof MATa and a/α cells grown vegetatively and in early meiotic conditions. This analysis identified over 1400 antisense ncRNAs, including 147 cases where antisense ncRNAs are differentially expressed in relation to the sense transcripts in different cell-types or growth conditions. Another subset of 65 genes express antisense ncRNA but not the sense transcript in the four conditions assayed here. These genes may be regulated by antisense transcription, and derepressed under other environmental conditions. There arealso over 300 examples of genes that express both sense and antisense transcripts at similar levels. In these cases, the antisense transcript may not have a role in regulating coding expression. This work shows that the non-coding transcriptome has an importantrole in differential cellular responses, and suggests cis-acting antisense transcription may be a widespread mechanism of regulation. |
