COPS5 and retinitis pigmentosa 1: Moreover, the intriguing regulatory mechanism of PRPF8 on Brr2 helicase activity through the PRPF8 Jab1/MPN domain and its extending tail, where the RP type 13 (RP13) causative mutations accumulate, with unclear role in the spliceosome function and splicing, highlights PRPF8 as an important candidate to help us gain insight into spliceosome function and RP pathomechanism.