User:Integrated science guy/Brr2

Brr2

BACKGROUND

Brr2 belongs to a family termed DExD/H box proteins and is required for catalytic activation and disassembly of the spliceosome. The spliceosome is a highly dyn amic RNA protein machine that requiring the ordered binding and release of five small nuclear ribonuclear proteins(snRNPS)to the intron containing pre-Mrna. It has been shown that Brr2 can separate U4 and U6 snRNPS from a RNP-complex consisting of U1,U2,U5 and U4/U6 snRNPS ; which is pivotal for the recycling of the spliceosome.

STRUCTURE

In is important to look at the association of U4/U6; which forms a phylogenetically highly conserved Y-shaped interaction domain, consisting of two intermolecular helices (stem1 and stem2) .This association enables us To better understand how Brr2 catalytically unwinds the RNA, thus dissociating U4/U6 resulting in free U4. We must examine the structural characteristics of this large spliceosomal protein (246KDa in yeast). It contains a N-terminal region, where it is predicted to lack tertiary structure and a tandem repeat of helical cassettes, where both cassettes contain dual Rec A domains and a portion that resembles the sec63p sub-unit of the ER. And on the other end the C-terminal sec63 unit of Brr2 contains three domains

MECHANISM/INTERACTIONS

By rational mutagenesis combined with U4/U6 di-snRNA unwinding assays it was shown how the Rec A domains and the sec 63 unit form a functional unit that is capable of unwinding RNA. The C-terminal region of Prp 8 has been demonstrated to bind to Brr2 creating a complex that is capable of successful linkage to U4/U6. It is believed that the motif in the first helicase domain is critical for ATPase function, cell viability and U4/U6 unwinding, where the second helicase domain can be altered without consequence.

The proposed mechanism of Brr2 is brought about by its H2 and S2 domains that share similarities to the Hel308 modules along with its N-terminal domain. The actual mechanics of the unwinding of the U4/U6 association requires disruption of base pairs via Brr2 helicase RNA and ATP.

BIOLOGICAL ROLE

The Brr2 yeast protein is a key component of the U5 snRNP, and it has been shown to mediate ATP dependent dissociation , when binding to form the complex termed the triple snurp (U4/U6 and U5). This tri-small nuclear ribonuclear protein is a highly conserved evolutionary spliceosome subunit. In order to accomplish the unnealling of the U4/U6 snRNA duplex, the U5 along with its components namely, but not limited to Brr2 must bind to the pre-established complex. In the cell the regeneration and dissociation of the snRNPS and proteins in the spliceosome are accomplished by an antagonistic association between prp24 and Brr2.

HOMOLOGS It has been shown recently that a number of spliceosome proteins have been shown to be conserved from yeast to humans. Brr2 is the yeast homolog of the hU5-200k.This was identified by the cold-sensitive mutant Brr2-1 which was shown in the experiment to be ineffective for pre-Mrna splcing .The U4/U6U5 tri-snRNP are unwound by the RNA helicase Brr2/U5-200k by the same mechanism. Like Brr2 it has been shown that U5-200k has conserved domains, such as the DEAD/DEAH box helicases and Sec63 domains and displays a strong interaction with U5 snRNA.

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