Transcription of the Schizosaccharomyces pombe U2 gene in vivo and in vitro is directed by two essential promoter elements

As compared to the metazoan small nuclear RNAs (snRNAs), relatively little is known about snRNA synthesis in unicellular organisms. We have analyzed t he transcription of the Schizosaccharomyces pombe U2 snRNA gene in vivo and in the homologous in vitro system. Deletion and linker-scanning analyses s how that the S.pombe U2 promoter contains at least two elements: the spUSE centered at -55, which functions as an activator, and a TATA box at -26, wh ich is essential for basal transcription. These data point to a similar arc hitecture among S.pombe, plant and invertebrate snRNA promoters. Factors re cognizing the spUSE can be detected in whole cell extracts by DNase I footp rinting and competition studies show that the binding of these factors corr elates with transcriptional activity. Electrophoretic mobility shift assays and gel-filtration chromatography revealed a native molecular mass of simi lar to 200 kDa for the spUSE binding activity. Two polypeptides of molecula r masses 25 and 65 kDa were purified by virtue of their ability to specific ally bind the spUSE.