Analysis of 5' and 3' snoRNA termini maturation in Saccharomyces cerevisiae

Abstract

Small nucleolar RNAs (snoRNAs) are the best characterized non‐coding RNAs transcribed by RNA polymerase II. They are produced as precursors, whose extended 3' ends are trimmed exonucleolytically, whereas 5' ends either undergo combined endo‐ and exonucleolytic processing by Rnt1 and Rat1, respectively, or remain unchanged. In the latter case, the m7G cap becomes hypermethylated by Tgs1. [figure1]cRT‐PCR analyses suggest that processing of snoRNA 3' and 5' termini is tightly coupled. Inhibition of 5' end maturation, in rnt1Δ strain, cause the accumulation of snoRNA precursors that don't possess mature 3' ends but carry polyadenylated extensions. This defect is further increased when components of the cap‐binding complex (CBC) or methyltransferase Tgs1 are missing. Although we observe an accumulation of pre‐snoRNAs in rnt1Δ strain, there are also mature snoRNAs present. These results, obtained in Northern blot analysis, suggest the existence of an alternative pathway of 5' end processing, that most likely involves pre‐snoRNA cap removal by Dcp1/Dcp2 complex. Interestingly most pre‐snoRNAs that accumulates in dcp2Δ strain, are not cleaved by Rnt1, which was confirmed by 5´ RACE analysis.Obtained data strongly suggest the existence of a quality control mechanism that coordinates 5' and 3' end processing.Research project was financially supported by by “Generacja Przyszłości” Ministry of Science and Higher Education Funding Programme.