Chanfreau G, Rotondo G, Legrain P, Jacquier A
Laboratoire du Métabolisme des ARN, URA1300 CNRS, Institut Pasteur, Departement des Biotechnologies, 25 rue du Dr Roux, F-75724 Paris Cedex 15, France.
EMBO J. 1998 Jul 1;17(13):3726-37. doi: 10.1093/emboj/17.13.3726.
Small nucleolar RNAs (snoRNAs) are intron encoded or expressed from monocistronic independent transcription units, or, in the case of plants, from polycistronic clusters. We show that the snR190 and U14 snoRNAs from the yeast Saccharomyces cerevisiae are co-transcribed as a dicistronic precursor which is processed by the RNA endonuclease Rnt1, the yeast ortholog of bacterial RNase III. RNT1 disruption results in a dramatic decrease in the levels of mature U14 and snR190 and in accumulation of dicistronic snR190-U14 RNAs. Addition of recombinant Rnt1 to yeast extracts made from RNT1 disruptants induces the chase of dicistronic RNAs into mature snoRNAs, showing that dicistronic RNAs correspond to functional precursors stalled in the processing pathway. Rnt1 cleaves a dicistronic transcript in vitro in the absence of other factors, separating snR190 from U14. Thus, one of the functions of eukaryotic RNase III is, as for the bacterial enzyme, to liberate monocistronic RNAs from polycistronic transcripts.
小核仁RNA（snoRNA）由内含子编码，或从单顺反子独立转录单元表达，在植物中则从多顺反子簇表达。我们发现，酿酒酵母中的snR190和U14 snoRNA作为双顺反子前体共同转录，该前体由RNA内切核酸酶Rnt1加工，Rnt1是细菌RNase III在酵母中的同源物。RNT1基因敲除导致成熟U14和snR190水平显著下降，双顺反子snR190 - U14 RNA积累。将重组Rnt1添加到由RNT1基因敲除菌株制备的酵母提取物中，可促使双顺反子RNA转化为成熟的snoRNA，这表明双顺反子RNA对应于加工途径中停滞的功能性前体。在没有其他因子的情况下，Rnt1可在体外切割双顺反子转录本，将snR190与U14分离。因此，真核生物RNase III的功能之一，与细菌酶一样，是从多顺反子转录本中释放单顺反子RNA。
