Polymerase Selectivity and the Promoters of U snRNA Genes

Abstract

The U small nuclear RNAs (snRNAs) form a functionally conserved family of RNAs found in eukaryotic cells. A subset of these RNAs, the spliceosomal snRNAs, function in the removal of introns from messenger RNA precursors. In most eukaryotes this group of snRNAs are U1, U2, U4, U5 and U6 but in trypanosomes, which produce mature mRNAs by transrather than cis-splicing, no homologues of U1 or U5 have been found (see Guthrie and Patterson 1988; Lamond et al. 1990 for reviews). Another ubiquitous member of the U snRNA family which will be discussed here is U3. U3 is found in the nucleolus rather than the nucleoplasm and is involved in the processing of ribosomal RNA precursors (Kass et al. 1990). The topic of this review will not, however, be the function of these RNAs, what will interest us is their transcription.