The ribonucleotidyl transferase USIP-1 acts with SART3 to promote U6 snRNA recycling.
Bottom Line: Their reutilization for subsequent rounds of splicing requires reversion to their original configurations, but little is known about this process.Here, we show that ZK863.4/USIP-1 (U Six snRNA-Interacting Protein-1) is a ribonucleotidyl transferase that promotes accumulation of the Caenorhabditis elegans U6 snRNA.Endogenous USIP-1-U6 snRNA complexes lack the Lsm proteins that constitute the protein core of the U6 snRNP, but contain the U6 snRNP recycling factor SART3/B0035.12.
Affiliation: Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, CH-4058 Basel, Switzerland University of Basel, Petersplatz 1, CH-4003 Basel, Switzerland.Show MeSH
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Mentions: Whereas the splicing process and mechanisms of spliceosome activation are understood in substantial detail, much less is known about processes that promote reutilization of the spliceosome for additional rounds of splicing (1). We propose here that USIP-1 is a novel U6 snRNA recycling factor. We note that at this point we cannot formally exclude a role of USIP-1 in U6 snRNA biogenesis. However, the fact that USIP-1 interacts both physically and genetically with a bona fide U6 snRNA recycling factor strongly implies that U6 snRNA recycling is a major function of USIP-1. Indeed, when integrating the results that we present in the current study with previous data on U4/U6 di-snRNP regeneration (5,8,9,51), a U6 snRNA recycling pathway begins to emerge (Figure 7). In particular, we propose that USIP-1 binds to ‘post-spliceosomal’ U6 snRNA, devoid of Lsm proteins. Subsequently or coincidentally, SART3 is recruited to this complex. The complex then matures to acquire Lsm proteins as well as the U4 snRNP (24,27,29), associated with Sm proteins, while ejecting USIP-1.
Affiliation: Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, CH-4058 Basel, Switzerland University of Basel, Petersplatz 1, CH-4003 Basel, Switzerland.