The <I>SDB23</I> gene of <I>Saccharomyces cerevisiae</I> was isolated in a search for high copy-number suppressors of mutations in a cell cycle gene, <I>DBF2. SDB23</I> encodes a 21,276 Da protein with significant sequence similarity to characterised mammalian and yeast snRNP core proteins. Examination of multiple sequence alignments of snRNP core proteins with Sdb23p indicates that the amino-termini of all these proteins share a number of highly conserved residues, and identifies a novel motif characteristic of snRNP core proteins. In contrast, the carboxy-termini of these proteins diverge considerably. An exceptionally hydrophilic, asparagine-rich carboxy-terminus distinguishes Sdb23p from the characterised snRNP core proteins, which tend to have an abundance of arginine and glycine residues. Sdb23p is essential for cell growth and is required for nuclear pre-mRNA splicing both <I>in vivo</I> and <I>in vitro</I>. Extracts prepared from Sdb23p-depleted cells are unable to support splicing and have vastly reduced levels of U6 snRNA. The stability of U1, U2, U4 and U5 spliceosomal snRNAs is not affected by the loss of Sdb23p. Overexpression of U6 snRNA can partially compensate for the loss of Sdb23p, indicating that one role of this protein is to stabilise free U6. However, the partial nature of this suppression would suggest that Uss1p has an additional, as yet uncharacterised role. Based on <I>in vitro</I> and <I>in vivo</I> characterisation of <I>SDB23</I>, this gene encodes a novel U6 snRNA-associated polypeptide, related to the mammalian snRNP core proteins, that is essential for nuclear pre-mRNA splicing and U6 snRNA stability. Sdb23p appears to represent a previously unidentified class of U6 snRNP-associated core-like proteins. For this reason, <I>SDB23</I> has been given the more logical name <I>USS1</I> (<I>U-S</I>ix <I>S</I>nRNP), as its original name was based on its uncharacterised suppressor activity.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:643409 |
| Date | January 1995 |
| Creators | Cooper, Michelle |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/13460 |
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