Abstract
In addition to protein-coding genes, RNA polymerase II (pol II) transcribes numerous genes for non-coding RNAs, including the small-nuclear (sn)RNA genes. snRNAs are an important class of non-coding RNAs, several of which are involved in pre-mRNA splicing. The molecular mechanisms underlying expression of human pol II-transcribed snRNA genes are less well characterized than for protein-coding genes and there are important differences in expression of these two gene types. Here, we review the DNA features and proteins required for efficient transcription of snRNA genes and co-transcriptional 3′ end formation of the transcripts.
Highlights
RNA polymerase II is responsible for the transcription of all 25 000 or so protein-coding genes in the human genome
Transcription factors Oct1, Sp1, NF1 and Staf bind to sequences in the distal sequence element (DSE), which has the properties of a transcriptional enhancer [2,21]
PTF helps to recruit the TATA-binding protein (TBP) and the TBP-associated factors (TAFs) that make up the snRNA TAF complex to the polymerase II (pol II)-transcribed snRNA genes [22,26,27]
Summary
RNA polymerase II (pol II) is responsible for the transcription of all 25 000 or so protein-coding genes in the human genome. SnRNAs are short RNAs (less than 350 nts) that associate with proteins to form small nuclear ribonucleoprotein particles (snRNPs) [6] Due to their roles in pre-mRNA splicing, the pol II-transcribed U1, U2, U4, U4atac, U5, U11 and U12 snRNAs are required for expression of intron-containing protein-coding genes. The pol III-transcribed genes for 7SK snRNA and U6 snRNA have a DSE and PSE, but in addition they have a TATA box at 225 [2]. Placing a TATA box downstream of the PSE in a pol II-transcribed snRNA gene converts transcription from pol II to pol III [2], emphasizing that the DSE and PSE can work as cis-acting elements for either polymerase. We review what is currently known about expression of human snRNA genes transcribed by pol II and the future prospects of a complete understanding of the mechanisms involved
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