Transcriptional regulation by non-coding RNAs in Saccharomyces cerevisiae

Thesis

Genome-wide studies in Saccharomyces cerevisiae have revealed that the majority of the genome is transcribed on both strands, producing both coding and non-coding RNAs (ncRNAs). Initially, these ncRNAs were regarded as spurious transcripts but some have since been shown to have important roles as transcriptional regulators. Very little is understood about how ncRNAs are initiated, terminated and processed or how this influences their function. To address these questions, the expression, stability, and subcellular localization of the ncRNAs at the endogenous GAL locus was analysed. This revealed a complex interleaved transcript map, challenging the conventional view of a transcription unit (TU) flanked by 5’ sequences or promoters (P) that initiate transcription and 3’ regions, known as terminators (T), which control events such as transcript cleavage, polyadenylation, export and transcription termination. By creating conventional (PGAL-T) or unconventional (PGAL-P) hybrid TUs at the GAL locus, in which a promoter or terminator is positioned downstream of a galactose-inducible promoter, this work shows that both promoters and terminators are able to initiate antisense transcription to yield stable antisense transcripts. The data suggest that terminators contribute to efficient but variable expression from the promoter. An unconventional P-P TU, lacking a terminator, is transcribed on both strands but the sense transcript remains at low levels, through the repressive action of antisense transcription, and is retained in the nucleus. In contrast, the conventional P-T bi-directional TUs are plastic, with the Rrp6 component of the nuclear exosome and TATA-like sequences in the 3’ UTR determining whether the predominant transcript is antisense or sense. By relieving the repressive action of antisense transcription, this allows high levels of sense transcript to accumulate in the cytoplasm, contributing to gene expression, supporting a novel mode of gene regulation involving components of RNA quality control pathways acting through the 3’ region of genes.

Authors: Serra Barros, A; Ana Cristina Serra Barros

• Publication date: 2012
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: Oxford University, UK
• Language: English
• Keywords: S. cerevisiae; non-coding RNAs; transcription
• Subjects: Genetics (life sciences); Life Sciences; Biochemistry