Prp24: Difference between revisions

U6 is arguably the most structurally dynamic snRNA involved in the splicing process, seemingly undergoing at least three different structures: it exists in one conformation as free U6 snRNP, another when base paired in the U4/U6 di-snRNP, and a third in base pairing interactions with U2 and the 5' splice site <ref name="Jandrositz"/>.  One large role suggested for Prp24 has been in assisting in the conformational changes between the free U6 structure and the U4/U6 conformation.

Prp24 coimmunoprecipitates with free U6 and U4/U6 di-snRNP, indicating that it is closely associated with these structures <ref name="Shannon"/><ref name="Ghetti">PMID:7585243</ref>.  Initial investigation revealed that Prp24 binds within the 30-56 nucleotide region of free U6, as well as to stem II of U4/U6 in the 39-56 and 67-70 nucleotide regions of U6 <ref name="Ghetti"/>.  Further investigation of the structure showed that Prp24 very likely binds directly to the 40-43 nucleotides of U6 based on chemical modification of naked U6 snRNA compared to free U6 snRNP<ref name="Jandrositz"/>.   

The interactions of Prp24 with U6 and U4/U6 are very important in proper spliceosome assembly, as evidenced by mutations in Prp24 that suppress mutations in U6 or U4.  Mutations in RRM 2 and RRM 3 suppress the effects of mutations in the 3' stem of U6, in a region termed the telestem <ref name="Vidaver"/>.  A later study showed that RRM 1 binds with high affinity to U6 and is important in interactions with mutations in the 3' region of U6 <ref name="Kwan"/>.  Mutations in two RNP consensus domains of Prp24 suppress the effects of mutations in U4 in the stem II region of U4/U6 <ref name="Shannon"/>.  Truncation and deletion of internal segments of U6 showed that the central region of U6 is the most important region for interaction with Prp24 and that RRM 1 and RRM 2 are the likely portions of Prp24 that interact with U6 in this region <ref name="Kwan"/>.  Deletion of conserved residues in the C-terminal domain of Prp24 caused temperature sensitive growth and reduced levels of U4/U6, suggesting that this region too, containing the fourth RRM, is important for interactions in assembly of the spliceosome <ref name="Rader"/>.

NMR analysis of fragments of U6 sequence and regions of Prp24 have further defined and supported the interactions of the protein with U6 snRNA.  Analysis of an RNA oligonucleotide containing sequences identical to nucleotides 41-46 and 83-88 of U6 (the regions proposed to bind to Prp24) with a truncated protein containing RRMs 1 and 2 of Prp24 showed that these RRMs interacted sequence specifically with these nucleotides <ref name="Bae"/>.  Another NMR study identified sequence specific interaction of <scene name='Sandbox_Reserved_340/2kh9/3'>RRM 2 with RNA</scene>, and it was determined from this that most likely region of U6 for interaction was the AGAGAU sequence of nucleotides 49-54, within the region of previously predicted interaction <ref name="Martin">PMID:20181740</ref>.  From this, it was predicted that RRM 1 would interact with the GAUCAG sequence of nucleotides 55-60 <ref name="Martin"/>.