The splicing factor PRP2, a putative RNA helicase, interacts directly with pre‐mRNA.

The RNA helicase‐like splicing factor PRP2 interacts only transiently with spliceosomes. To facilitate analysis of interactions of PRP2 with spliceosomal components, PRP2 protein was stalled in splicing complexes by two different methods. A dominant negative mutant form of PRP2 protein, which associates stably with spliceosomes, was found to interact directly with pre‐mRNAs, as demonstrated by UV‐crosslinking experiments. The use of various mutant and truncated pre‐mRNAs revealed that this interaction requires a spliceable pre‐mRNA and an assembled spliceosome; a 3′ splice site is not required. To extend these observations to the wild‐type PRP2 protein, spliceosomes were depleted of ATP; PRP2 protein interacts with pre‐mRNA in these spliceosomes in an ATP‐independent fashion. Comparison of RNA binding by PRP2 protein in the presence of ATP or gamma S‐ATP showed that ATP hydrolysis rather than mere ATP binding is required to release PRP2 protein from pre‐mRNA. As PRP2 is an RNA‐stimulated ATPase, these experiments strongly suggest that the pre‐mRNA is the native co‐factor stimulating ATP hydrolysis by PRP2 protein in spliceosomes. Since PRP2 is a putative RNA helicase, we propose that the pre‐mRNA is the target of RNA displacement activity of PRP2 protein, promoting the first step of splicing.