High impact information on PRP18

• The Mlp1-dependent leakage of intron-containing RNAs is increased in presence of ts-prp18 delta, a splicing mutant [1].
• We find that while the first step of splicing (cleavage at the 5' splice site, and generation of the exon 1 and lariat intermediates) is unaffected by the absence of PRP18, the second step of splicing (excision of the lariat intron and formation of mRNA) is substantially slower in the absence of PRP18 [2].
• Recently, the human homologs of Prp18 and Slu7 were identified [3].
• The most highly conserved region of Prp18, a nearly invariant stretch of 19 aa, forms part of a loop between two alpha-helices and may interact with the U5 small nuclear ribonucleoprotein particles [4].
• The RNA-dependent ATPase, Prp16p, functions at a stage in splicing when ATP is required, whereas Prp18p functions at an ATP-independent stage [5].

Biological context of PRP18

• Single alanine mutations of zinc knuckle residues Cys122, His130, and Cys135 had no effect on cell growth, but caused Slu7 function during pre-mRNA splicing in vitro to become dependent on Prp18 [6].
• Alanine cluster mutations of 215EIE217 and 221LELY224 abrogated Slu7 binding to Prp18 in a two-hybrid assay and in vitro, and elicited temperature-sensitive growth phenotypes in vivo [6].
• Quantitative polymerase chain reactions confirm the array-based finding that Prp17p and Prp18p are not dispensable for removal of introns with short branchpoint-to-3' splice site distances [7].

Anatomical context of PRP18

• Both complementation of extracts and chasing of the isolated prp18 spliceosomes takes place with micrococcal nuclease-treated extracts [8].

Physical interactions of PRP18

• We therefore suggest that the functional region of Prp17p that interacts with Prp18p, Prp16p, and U5 snRNA is the N terminal region of the protein [9].
• The structure suggests that one face of Prp18 interacts with the splicing factor Slu7, whereas the more evolutionarily conserved amino acids in Prp18 form the opposite face [4].

Other interactions of PRP18

• Only mutations in the N-terminal nonconserved domain of PRP17 are synthetically lethal in combination with mutations in PRP16 and PRP18, two other gene products required for the second splicing reaction [9].
• Deleted versions of Slu7 were also tested for interaction with Prp18 in the two-hybrid system [10].
• We show that the requirement for Prp18 during the second step of actin pre-mRNA splicing in vitro is dictated by the distance between the branch point and the 3'splice site [10].

Analytical, diagnostic and therapeutic context of PRP18

• Physical interaction between Slu7 and Prp18 was demonstrated by using the two-hybrid assay [10].
• Depletion/reconstitution studies coupled with immunoprecipitations suggest that second step factors are recruited to the spliceosome in the following order: Slu7 --> Prp18 --> Prp22 [6].

References