Biogenesi degli snoRNA in Saccharomyces cerevisiae: identificazione del promotore trascrizionale e di fattori richiesti per il processamento

snoRNAs (small nucleolar RNAs) are non-protein-coding RNAs and they are components of ribonucleoprotein particles (snoRNPs) involved in rRNA maturation as well as in other RNA modifications, in eukaryotic cells; its function is carried out in the nucleolus. snoRNA function is to guide the modification, or, in some cases, the endonucleolytic processing, of target RNA by base pairing, whereas catalytic activity is provided by one of snoRNP proteins. In S. cerevisiae, most snoRNA genes are independent transcription units: in this study we have identified promoter elements required for efficient transcription, both by comparative genomic analysis of snoRNA gene upstream regions in five species of Saccaromycetes, and by experimental analysis carried out by mutagenesis of some snoRNA gene upstream regions in S. cerevisiae. Processing of snR52, the only snoRNA transcribed by RNA polymerase III in S. cerevisiae, was also studied: it has been verified that snoRNP integrity is necessary for correct maturation of snR52, as previously observed for snoRNAs transcribed by RNA polymerase II.