Ubiquitin Specific Peptidase 39 (USP39)

The deduced 565-amino acid protein has a calculated molecular mass of 65.4 kD. The N-terminal domain is rich in arginine, serine, and glutamic acid and resembles the RS domain of SR-related proteins, such as SNRP70 and RY1. USP39 also contains a central zinc finger and 2 ubiquitin C-terminal hydrolase (UCH) domains. USP39 shares 65% amino acid similarity with yeast Sad1. Increasing amounts of anti-USP39 antibody resulted in accumulation of unspliced pre-mRNAs, suggesting that USP39 has a role in pre-mRNA splicing. Immunodepletion of USP39 strongly inhibited splicing. Immunoprecipitation at increasing salt concentrations demonstrated that USP39 was not required for stability of the U4/U6.U5 tri-snRNP but was essential for recruitment of the tri-snRNP to the prespliceosome.