Prp8: Difference between revisions

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Following suit with its unique structural makeup, Prp8 also possesses the potential to perform a variety of functions at the heart of the spliceosome. Above all else, Prp8 has been strongly implicated as a large scaffold which coordinates the active catalytic components of the spliceosome <ref name='Prp8: At the heart of the spliceosome'>DOI:10.1261/rna.2220705</ref>. Prp8 acts as a cofactor for RNA splicing because it is required for the formation of the active (complex B*) spliceosome and for subsequent first and second transesterification reactions <ref name='Prp8: At the heart of the spliceosome'>DOI:10.1261/rna.2220705</ref>. Prp8's bromodomain has been evolutionarily modified to recognize acetylated lysine residues, and given that many spliceosomal proteins are acetylated at lysine residues, it is likely that Prp8 mediates the assembly of spliceosome proteins and protein-RNA contacts through recognition of the lysine residues <ref name='Prp8, the pivotal protein of the spliceosomal catalytic center, evolved from a retroelement-encoded reverse transcriptase'>PMID:21441348 </ref>. One example of such an interaction is Prp8's bromodomain mediated contact with Snu114p, which is a GTPase involved in RNA remodeling during the catalytic cycle of splicing <ref name='Prp8, the pivotal protein of the spliceosomal catalytic center, evolved from a retroelement-encoded reverse transcriptase'>PMID:21441348 </ref>.

Prp8's modified reverse transcritase and RNase H-like domains are postulated to function as recognition, interaction, and handover domains for snRNAs catalytically active in the spliceosome and portions of the pre-mRNA substrate <ref name='Mechanism for aar2p function as a U5 snRNP assembly factor'>PMID:21764848</ref>. Crosslinking experiments have shown that U5 and U6 snRNAs, as well as the GU dinucleotide of the 5' splice site, polypyrimidine tract (close to the intron branch point), and the 3' splice site all interact with or close to the reverse transcriptase and RNase H-like domains of Prp8 which supports the scaffolding and coordination role of Prp8 in pre-mRNA splicing <ref name='Structure and function of an RNase H domain at the heart of the spliceosome'>DOI:10.1038/emboj.2008.209</ref><ref name='splicing factor prp8 governs u4/u6 rna unwinding'>PMID:10024880</ref><ref name='roles of prp8 protein in the assembly of splicing complexes'>PMID:1396567<ref>. Therefore, in sequence with the events of pre-mRNA splicing, Prp8 cooperates with Prp28 by bringing it into contact with the 5' splice site and coordinating Prp28's trans-helicase activity to handover the 5' splice site to U6 <ref name='Structure and function of an RNase H domain at the heart of the spliceosome'>DOI:10.1038/emboj.2008.209</ref>. However, to complete the hand over and activation of the catalytic cycle the U4/U6 di-snRNP must be unwound. Prp8 also coordinates this event because Aar2p binds the RNase domain of Prp8 which sequesters the MPN/Jab1 domain, however when Aar2p is phosphorylated, Brr2 is able to interact withe the released C-terminus, which activates Brr2's helicase activity allowing for the unwinding of U4 and U6, and subsequently the 5' splice site handover and catalytic activation of the first step of pre-mRNA splicing <ref name='Mechanism for aar2p function as a U5 snRNP assembly factor'>PMID:21764848</ref>. The catalytic activity of the spliceosome is also potentially coordinated by Prp8 which is explained by the 'lock and load' hypothesis which is as follows; following the 5' splice site activation, the first transesterification step is carried out, and Prp8 subsequently locks the 5' splice site into position and loads the 3' splice site into position for catalysis of the second transesterification step and subsequent completion of the splicing cycle <ref name='Prp8: At the heart of the spliceosome'>DOI:10.1261/rna.2220705</ref>. This is all thought to be facilitated by Prp8's modified domains that don't retain any of their rudimentary catalytic functions, and are instead specialized only for RNA/protein binding and coordination.

Prp8's modified reverse transcritase and RNase H-like domains are postulated to function as recognition, interaction, and handover domains for snRNAs catalytically active in the spliceosome and portions of the pre-mRNA substrate <ref name='Mechanism for aar2p function as a U5 snRNP assembly factor'>PMID:21764848</ref>. Crosslinking experiments have shown that U5 and U6 snRNAs, as well as the GU dinucleotide of the 5' splice site, polypyrimidine tract (close to the intron branch point), and the 3' splice site all interact with or close to the reverse transcriptase and RNase H-like domains of Prp8 which supports the scaffolding and coordination role of Prp8 in pre-mRNA splicing <ref name='Structure and function of an RNase H domain at the heart of the spliceosome'>DOI:10.1038/emboj.2008.209</ref><ref name='splicing factor prp8 governs u4/u6 rna unwinding'>PMID:10024880</ref><ref name='roles of prp8 protein in the assembly of splicing complexes'>PMID:1396567</ref>. Therefore, in sequence with the events of pre-mRNA splicing, Prp8 cooperates with Prp28 by bringing it into contact with the 5' splice site and coordinating Prp28's trans-helicase activity to handover the 5' splice site to U6 <ref name='Structure and function of an RNase H domain at the heart of the spliceosome'>DOI:10.1038/emboj.2008.209</ref>. However, to complete the hand over and activation of the catalytic cycle the U4/U6 di-snRNP must be unwound. Prp8 also coordinates this event because Aar2p binds the RNase domain of Prp8 which sequesters the MPN/Jab1 domain, however when Aar2p is phosphorylated, Brr2 is able to interact withe the released C-terminus, which activates Brr2's helicase activity allowing for the unwinding of U4 and U6, and subsequently the 5' splice site handover and catalytic activation of the first step of pre-mRNA splicing <ref name='Mechanism for aar2p function as a U5 snRNP assembly factor'>PMID:21764848</ref>. The catalytic activity of the spliceosome is also potentially coordinated by Prp8 which is explained by the 'lock and load' hypothesis which is as follows; following the 5' splice site activation, the first transesterification step is carried out, and Prp8 subsequently locks the 5' splice site into position and loads the 3' splice site into position for catalysis of the second transesterification step and subsequent completion of the splicing cycle <ref name='Prp8: At the heart of the spliceosome'>DOI:10.1261/rna.2220705</ref>. This is all thought to be facilitated by Prp8's modified domains that don't retain any of their rudimentary catalytic functions, and are instead specialized only for RNA/protein binding and coordination.

=Evolution of Prp8=

=References=

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 Following suit with its unique structural makeup, Prp8 also possesses the potential to perform a variety of functions at the heart of the spliceosome. Above all else, Prp8 has been strongly implicated as a large scaffold which coordinates the active catalytic components of the spliceosome <ref name='Prp8: At the heart of the spliceosome'>DOI:10.1261/rna.2220705</ref>. Prp8 acts as a cofactor for RNA splicing because it is required for the formation of the active (complex B*) spliceosome and for subsequent first and second transesterification reactions <ref name='Prp8: At the heart of the spliceosome'>DOI:10.1261/rna.2220705</ref>. Prp8's bromodomain has been evolutionarily modified to recognize acetylated lysine residues, and given that many spliceosomal proteins are acetylated at lysine residues, it is likely that Prp8 mediates the assembly of spliceosome proteins and protein-RNA contacts through recognition of the lysine residues <ref name='Prp8, the pivotal protein of the spliceosomal catalytic center, evolved from a retroelement-encoded reverse transcriptase'>PMID:21441348 </ref>. One example of such an interaction is Prp8's bromodomain mediated contact with Snu114p, which is a GTPase involved in RNA remodeling during the catalytic cycle of splicing <ref name='Prp8, the pivotal protein of the spliceosomal catalytic center, evolved from a retroelement-encoded reverse transcriptase'>PMID:21441348 </ref>.
-Prp8's modified reverse transcritase and RNase H-like domains are postulated to function as recognition, interaction, and handover domains for snRNAs catalytically active in the spliceosome and portions of the pre-mRNA substrate <ref name='Mechanism for aar2p function as a U5 snRNP assembly factor'>PMID:21764848</ref>. Crosslinking experiments have shown that U5 and U6 snRNAs, as well as the GU dinucleotide of the 5' splice site, polypyrimidine tract (close to the intron branch point), and the 3' splice site all interact with or close to the reverse transcriptase and RNase H-like domains of Prp8 which supports the scaffolding and coordination role of Prp8 in pre-mRNA splicing <ref name='Structure and function of an RNase H domain at the heart of the spliceosome'>DOI:10.1038/emboj.2008.209</ref><ref name='splicing factor prp8 governs u4/u6 rna unwinding'>PMID:10024880</ref><ref name='roles of prp8 protein in the assembly of splicing complexes'>PMID:1396567<ref>. Therefore, in sequence with the events of pre-mRNA splicing, Prp8 cooperates with Prp28 by bringing it into contact with the 5' splice site and coordinating Prp28's trans-helicase activity to handover the 5' splice site to U6 <ref name='Structure and function of an RNase H domain at the heart of the spliceosome'>DOI:10.1038/emboj.2008.209</ref>. However, to complete the hand over and activation of the catalytic cycle the U4/U6 di-snRNP must be unwound. Prp8 also coordinates this event because Aar2p binds the RNase domain of Prp8 which sequesters the MPN/Jab1 domain, however when Aar2p is phosphorylated, Brr2 is able to interact withe the released C-terminus, which activates Brr2's helicase activity allowing for the unwinding of U4 and U6, and subsequently the 5' splice site handover and catalytic activation of the first step of pre-mRNA splicing <ref name='Mechanism for aar2p function as a U5 snRNP assembly factor'>PMID:21764848</ref>. The catalytic activity of the spliceosome is also potentially coordinated by Prp8 which is explained by the 'lock and load' hypothesis which is as follows; following the 5' splice site activation, the first transesterification step is carried out, and Prp8 subsequently locks the 5' splice site into position and loads the 3' splice site into position for catalysis of the second transesterification step and subsequent completion of the splicing cycle <ref name='Prp8: At the heart of the spliceosome'>DOI:10.1261/rna.2220705</ref>. This is all thought to be facilitated by Prp8's modified domains that don't retain any of their rudimentary catalytic functions, and are instead specialized only for RNA/protein binding and coordination.
+Prp8's modified reverse transcritase and RNase H-like domains are postulated to function as recognition, interaction, and handover domains for snRNAs catalytically active in the spliceosome and portions of the pre-mRNA substrate <ref name='Mechanism for aar2p function as a U5 snRNP assembly factor'>PMID:21764848</ref>. Crosslinking experiments have shown that U5 and U6 snRNAs, as well as the GU dinucleotide of the 5' splice site, polypyrimidine tract (close to the intron branch point), and the 3' splice site all interact with or close to the reverse transcriptase and RNase H-like domains of Prp8 which supports the scaffolding and coordination role of Prp8 in pre-mRNA splicing <ref name='Structure and function of an RNase H domain at the heart of the spliceosome'>DOI:10.1038/emboj.2008.209</ref><ref name='splicing factor prp8 governs u4/u6 rna unwinding'>PMID:10024880</ref><ref name='roles of prp8 protein in the assembly of splicing complexes'>PMID:1396567</ref>. Therefore, in sequence with the events of pre-mRNA splicing, Prp8 cooperates with Prp28 by bringing it into contact with the 5' splice site and coordinating Prp28's trans-helicase activity to handover the 5' splice site to U6 <ref name='Structure and function of an RNase H domain at the heart of the spliceosome'>DOI:10.1038/emboj.2008.209</ref>. However, to complete the hand over and activation of the catalytic cycle the U4/U6 di-snRNP must be unwound. Prp8 also coordinates this event because Aar2p binds the RNase domain of Prp8 which sequesters the MPN/Jab1 domain, however when Aar2p is phosphorylated, Brr2 is able to interact withe the released C-terminus, which activates Brr2's helicase activity allowing for the unwinding of U4 and U6, and subsequently the 5' splice site handover and catalytic activation of the first step of pre-mRNA splicing <ref name='Mechanism for aar2p function as a U5 snRNP assembly factor'>PMID:21764848</ref>. The catalytic activity of the spliceosome is also potentially coordinated by Prp8 which is explained by the 'lock and load' hypothesis which is as follows; following the 5' splice site activation, the first transesterification step is carried out, and Prp8 subsequently locks the 5' splice site into position and loads the 3' splice site into position for catalysis of the second transesterification step and subsequent completion of the splicing cycle <ref name='Prp8: At the heart of the spliceosome'>DOI:10.1261/rna.2220705</ref>. This is all thought to be facilitated by Prp8's modified domains that don't retain any of their rudimentary catalytic functions, and are instead specialized only for RNA/protein binding and coordination.
 =Evolution of Prp8=
 =References=
 <references/>