View source for Prp24

'''Prp24''' ('''p'''recursor '''R'''NA '''p'''rocessing, gene '''24''') is a protein part of the [[hnRNA|pre-messenger RNA]] [[RNA splicing|splicing]] process and aids the binding of [[U6 snRNA]] to [[U4 snRNA]] during the formation of [[spliceosome]]s. Found in [[eukaryotes]] from [[yeast]] to ''[[E. coli]]'', [[fungi]], and humans, Prp24 was initially discovered to be an important element of RNA splicing in 1989.<ref name="Bae">{{cite journal |last=Bae |first=E. |year=2007 |title=Structure and interactions of the first three RNA recognition motifs of splicing factor Prp24 |journal=Journal of Molecular Biology |volume=367 |issue=5 |pages=1447–1458 |doi=10.1016/j.jmb.2007.01.078 |pmid=17320109 |pmc=1939982 |display-authors=etal}}</ref><ref name="Vijayraghauan et al 1999">{{cite journal |last=Vijayraghavan |first=U. |author2=Company, M. |author3=Abelson, J.  |year=1989 |title=Isolation and characterization of pre-mRNA splicing mutants of ''Saccharomyces cerevisiae'' |journal=Genes & Development |volume=3 |issue=8 |pages=1206–1216 |doi=10.1101/gad.3.8.1206 |pmid=2676722 |doi-access=free }}</ref>  [[Mutations]] in Prp24 were later discovered in 1991 to suppress [[mutation]]s in U4 that resulted in cold-sensitive strains of yeast, indicating its involvement in the reformation of the U4/U6 duplex after the catalytic steps of splicing.<ref name="Shannon and Guthrie 1991">{{cite journal |last=Shannon |first=K. W. |author2=Guthrie, C.  |year=1991 |title=Suppressors of U4 snRNA mutation define a novel U6 snRNP protein with RNA-binding motifs |journal=Genes & Development |volume=5 |issue=5 |pages=773–785 |doi=10.1101/gad.5.5.773 |pmid=1827420 |doi-access=free }}</ref>
[[File:Prp24 domains 1 and 2 image.jpg|thumbnail|right|Prp24 RRMs 1 and 2]]
==Biological Role==
The process of spliceosome formation involves the U4 and U6 [[snRNP]]s associating and forming a di-snRNP in the [[cell nucleus]]. This di-snRNP then recruits another member ([[U5 snRNA|U5]]) to become a tri-snRNP. U6 must then dissociate from U4 to bond with [[U2 snRNA|U2]] and become catalytically active. Once splicing has been done, U6 must dissociate from the spliceosome and bond back with U4 to restart the cycle.
Prp24 has been shown to promote the binding of U4 and U6 snRNPs. Removing Prp24 results in the accumulation of free U4 and U6, and the subsequent addition of Prp24 regenerates U4/U6 and reduces the amount of free U4 and U6.<ref name="Raghunathan and Guthrie 1998">{{cite journal |last=Raghunathan |first=P. L. |author2=Guthrie, C. A.  |year=1998 |title=Spliceosomal Recycling Factor That Reanneals U4 and U6 Small Nuclear Ribonucleoprotein Particles |journal=[[Science (journal)|Science]] |volume=279 |issue=5352 |pages=857–860 |doi=10.1126/science.279.5352.857 |pmid=9452384|bibcode=1998Sci...279..857R }}</ref> Naked U6 snRNA is very compact and has little room to form [[base pair]]s with other RNA. However, when U6 snRNP associates with proteins such as Prp24, the structure is much more open, thus facilitating the binding to U4.<ref name="Karaduman">{{cite journal |last=Karaduman |first=R. |year=2006 |title=RNA Structure and RNA–Protein Interactions in Purified Yeast U6 snRNPs |journal=Journal of Molecular Biology |volume=356 |issue=5 |pages=1248–1262 |doi=10.1016/j.jmb.2005.12.013 |pmid=16410014 |display-authors=etal|hdl=11858/00-001M-0000-0012-E5F7-6 |hdl-access=free }}</ref>  Prp24 is not present in the U6/U4 duplex itself, and it has been suggested that Prp24 must leave the complex in order for proper base pairs to be formed.<ref name="Vidal">{{cite journal |last=Vidal |first=V. P. |year=1995 |title=Characterization of U6 snRNA-protein interactions |journal=RNA |volume=5 |issue=11 |pages=1470–1481 |doi= 10.1017/S1355838299991355|url=http://rnajournal.cshlp.org/content/5/11/1470.abstract |pmid=10580475 |pmc=1369868 |display-authors=etal}}</ref><ref name="Jandrositz and Guthrie 1995">{{cite journal |last=Jandrositz |first=A. |author2=Guthrie, A.  |year=1995 |title=Evidence for a Prp24 binding site in U6 snRNA and in a putative intermediate in the annealing of U6 and U4 snRNAs |journal=The EMBO Journal |volume=14 |issue=4 |pages=820–832 |pmc=398149 |pmid=7882985 |doi=10.1002/j.1460-2075.1995.tb07060.x }}</ref> It has also been suggested that Prp24 may play a role in destabilizing U4/U6 in order for U6 to pair bases with U2.<ref name="Vidaver et al 1999">{{cite journal |last1=Vidaver |first1=R. M. |year=1999 |title=Multiple functions of Saccharomyces cerevisiae splicing protein Prp24 in U6 RNA structural rearrangements |journal=Genetics |volume=153 |issue=3 |pages=1205–1218 |url=http://www.genetics.org/cgi/content/abstract/153/3/1205 |pmid=10545453 |last2=Fortner |first2=DM |last3=Loos-Austin |first3=LS |last4=Brow |first4=DA |doi=10.1093/genetics/153.3.1205 |pmc=1460831 }}</ref>
==Structure==
[[File:Prp24 domain 3.jpg|thumbnail|right|Prp 24 RRM 3]]
Prp24 has a [[molecular weight]] of 50 [[kDa]] and has been shown to contain four RNA recognition [[structural motif|motifs]] (RRMs) and a [[conserved sequence|conserved 12-amino acid sequence]] at the [[C-terminus]].<ref name="Karadumann">{{cite journal |last=Karaduman |first=R. |year=2008 |title=Structure of yeast U6 snRNPs: Arrangement of Prp24p and the LSm complex as revealed by electron microscopy |journal=RNA |volume=14 |issue=12 |pages=1–10 |doi=10.1261/rna.1369808 |pmid=18971323 |pmc=2590955 |display-authors=etal}}</ref><ref name="Rader">{{cite journal |doi=10.1017/S1355838202020010 |last=Rader |first=S. D. |author2=Guthrie, C.  |year=2002 |title=A conserved Lsm-interaction motif in Prp24 required for efficient U4/U6 di-snRNP formation |journal=RNA |volume=8 |issue=11 |pages=1378–1392 |pmc=1370345 |pmid=12458792 }}</ref> RRMs 1 and 2 have been shown to be important for high-[[Dissociation constant#Protein-ligand binding|affinity]] binding of U6, while RRMs 3 and 4 bind at lower affinity sites on U6.<ref name=Kwan>{{cite journal |last=Kwan |first=S. S. |author2=Brow, D. A.  |year=2005 |title=The N- and C-terminal RNA recognition motifs of splicing factor Prp24 have distinct functions in U6 RNA binding |journal=RNA |volume=11 |issue=5 |pages=808–820 |doi=10.1261/rna.2010905 |pmid=15811912 |pmc=1370765 }}</ref>  The first three RRMs interact extensively with each other and contain canonical folds that contain a four-stranded [[beta-sheet]] and two [[alpha helix|alpha-helices]]. The electropositive surface of RRMs 1 and 2 is a RNA [[Annealing (biology)|annealing]] domain while the cleft between RRMs 1 and 2 including the beta-sheet face of RRM2 is a sequence-specific RNA binding site.<ref name="Bae" /> The C-terminal motif is required for association with [[LSm]] proteins and contributes to [[Substrate (biochemistry)|substrate]] (U6) binding and not the catalytic rate of splicing<!--this last bit is nonsensical jargon-->.<ref name="Rader" />
[[File:U6 snRNP with Prp24 and Lsm.jpg|thumbnail|right|U6 snRNP with the associated Prp24 and LSm proteins]]
==Interactions==
Prp24 interacts with the U6 snRNA via its RRMs. It has been shown through [[chemical modification]] testing that [[nucleotides]] 39&ndash;57 of U6 (40&ndash;43 in particular)<ref name="Karaduman" /> are involved in binding Prp24.<ref name="Ghetti">{{cite journal |last=Ghetti |first=A. |author2=Company, M. |author3=Abelson, J.  |year=1995 |title=Specificity of Prp24 binding to RNA: a role for Prp24 in the dynamic interaction of U4 and U6 snRNAs |journal=RNA |volume=1 |issue=2 |pages=132–145 |pmc=1369067 |pmid=7585243 }}</ref>
The LSm proteins are in a consistent configuration on the U6 RNA.<ref name="Karadumann" />{{clarify|date=April 2009}}  It has been proposed that the LSm proteins and Prp24 interact both physically and functionally<ref name="Vidal" /> and the C-terminal motif of Prp24 is important for this interaction.<ref name="Rader" /> The binding of Prp24 to U6 is enhanced by the binding of Lsm proteins to U6, as is binding of U4 and U6.<ref name=Ryan>{{cite journal |doi=10.1017/S1355838202026092 |last=Ryan |first=D. E. |author2=Stevens, S. W. |author3=Abelson, J.  |year=2002 |title=The 5' and 3' domains of yeast U6 snRNA: Lsm proteins facilitate binding of Prp24 protein to the U6 telestem region |journal=RNA |volume=8 |issue=8 |pages=1011–1033 |pmc=1370313 |pmid=12212846 }}</ref> It was revealed by [[electron microscopy]] that Prp24 may interact with the LSm protein ring at LSm2.<ref name="Karadumann" />
==Homologs==
Prp24 has a human [[homology (biology)|homolog]], [[SART3]]. SART3 is a tumor rejection [[antigen]]<!--this makes it sound as if Prp24 is actually not found in humans--> (SART3 stands for "'''s'''quamous cell carcinoma '''a'''ntigen '''r'''ecognized by '''T''' cells, gene '''3'''). The RRMs 1 and 2 in yeast are similar to RRMs in human SART3.<ref name="Bae" /><ref name="Kwan" /> The C-terminal domain is also highly conserved from yeast to humans.<ref name="Bell">{{cite journal |last=Bell |first=M. |year=2002 |title=p110, a novel human U6 snRNP protein and U4/U6 snRNP recycling factor |journal=The EMBO Journal |volume=21 |issue=11 |pages=2724–2735 |doi=10.1093/emboj/21.11.2724 |pmid=12032085 |pmc=126028 |display-authors=etal}}</ref>  This protein, like Prp24, interacts with the LSm proteins<ref name="Karadumann" /><ref name="Stanek">{{cite journal |last=Stanek |first=D. |year=2003 |title=Targeting of U4/U6 small nuclear RNP assembly factor SART3/p110 to Cajal bodies |journal=Journal of Cell Biology |volume=160 |issue=4 |pages=505–516 |doi=10.1083/jcb.200210087    |pmid=12578909 |pmc=2173746 |display-authors=etal}}</ref> for the recycling of U6 into the U4/U6 snRNP. It has been proposed that SART3 target U6 to a [[Cajal body]] or a nuclear inclusion as the site of assembly of the U4/U6 snRNP<!--jargon-->.<ref name=Stanek/> SART3 is located on [[chromosome 12]], and a [[mutation]] is likely the cause of [[disseminated superficial actinic porokeratosis]].<ref name="urlOMIM - POROKERATOSIS, DISSEMINATED SUPERFICIAL ACTINIC, 1; DSAP1">{{cite web |url=https://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=175900 |title=OMIM - POROKERATOSIS, DISSEMINATED SUPERFICIAL ACTINIC, 1; DSAP1 |access-date=2009-04-05}}</ref>
==References==
{{Reflist|2}}
==External links==
*[https://web.archive.org/web/20090321165251/http://bssv01.lancs.ac.uk/ADS/BIOS336/336L10.html Biological Sciences at Lancaster University] Explanation of pre-mRNA splicing
[[Category:Gene expression]]
[[Category:Molecular genetics]]
[[Category:Spliceosome]]