| Summary: | <p>The molecular consequences of read-through transcription in <em>Saccharomyces cerevisiae</em> genes transcribed by RNA Polymerases I and II (Pol I and Pol II) are investigated in the two results sections of this thesis (Part I and Part II). In these studies, nascent and steady state RNA analyses are employed to evaluate transcriptional termination.</p> <p>Part I focuses on the impact that co-expressed Pol II transcribed genes can have on each other when placed in a convergent orientation. Transcriptional interference (TI), previously shown to occur between tandemly arranged genes, inhibits initiation of transcription on a downstream gene. These studies demonstrate that TI can also occur with <em>S.cerevisiae</em> Pol II genes arranged convergently. When the <em>GAL10</em> and <em>GAL7</em> genes are rearranged in a convergent orientation, transcriptional initiation occurs at full levels. However as soon as the two transcripts begin to overlap, elongation is restricted resulting in a severe reduction in steady state mRNA accumulation. This effect is only observed in the <em>cis</em> arrangement arguing against RNAi effects acting on the potential generation of antisense transcripts. These data reinforce the necessity to separate adjacent Pol II transcription units by efficient termination signals.</p> <p>Part II describes experiments that define the nascent termination site of Pol I transcribed rRNA genes. Furthermore, transcription run-on (TRO) analysis was performed on yeast strains in which specific factors involved in the Pol I transcription and RNA processing had been deleted. In particular, <em>S.cerevisiae</em> strains lacking the RPA12p subunit of Pol I have a severe defect in transcriptional termination at the nascent level indicating a direct role for this subunit in termination. Additionally, a yeast strain lacking Rnt1p, a protein involved in early rRNA processing, shows an altered transcriptional termination profile suggesting a link between processing and termination efficiency. In contrast to TI in Pol II, read-through transcription in Pol I may not significantly reduce rRNA gene synthesis.</p>
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