Eukaryotic snoRNAs: a paradigm for gene expression flexibility.
AbstractSmall nucleolar RNAs (snoRNAs) are one of the most ancient and numerous families of non-protein-coding RNAs (ncRNAs). The main function of snoRNAs – to guide site-specific rRNA modification – is the same in Archaea and all eukaryotic lineages. In contrast, as revealed by recent genomic and RNomic studies, their genomic organization and expression strategies are the most varied. Seemingly snoRNA coding units have adopted, in the course of evolution, all the possible ways of being transcribed, thus providing a unique paradigm of gene expression flexibility. By focusing on representative fungal, plant and animal genomes, we review here all the documented types of snoRNA gene organizati…
The transcription reinitiation properties of RNA polymerase III in the absence of transcription factors
AbstractTranscription reinitiation by RNA polymerase (Pol) III proceeds through facilitated recycling, a process by which the terminating Pol III, assisted by the transcription factors TFIIIB and TFIIIC, rapidly reloads onto the same transcription unit. To get further insight into the Pol III transcription mechanism, we analyzed the kinetics of transcription initiation and reinitiation of a simplified in vitro transcription system consisting only of Pol III and template DNA. The data indicates that, in the absence of transcription factors, first-round transcription initiation by Pol III proceeds at a normal rate, while facilitated reinitiation during subsequent cycles is compromised.
Promoter architecture and transcriptional regulation of Abf1-dependent ribosomal protein genes inSaccharomyces cerevisiae
In Saccharomyces cerevisiae, ribosomal protein gene (RPG) promoters display binding sites for either Rap1 or Abf1 transcription factors. Unlike Rap1-associated promoters, the small cohort of Abf1-dependent RPGs (Abf1-RPGs) has not been extensively investigated. We show that RPL3, RPL4B, RPP1A, RPS22B and RPS28A/B share a common promoter architecture, with an Abf1 site upstream of a conserved element matching the sequence recognized by Fhl1, a transcription factor which together with Ifh1 orchestrates Rap1-associated RPG regulation. Abf1 and Fhl1 promoter association was confirmed by ChIP and/or gel retardation assays. Mutational analysis revealed a more severe requirement of Abf1 than Fhl1 …