Error-Prone Splicing Controlled by the Ubiquitin Relative Hub1

Accurate pre-mRNA splicing is needed for correct gene expression and relies on faithful splice site recognition. Here, we show that the ubiquitin-like protein Hub1 binds to the DEAD-box helicase Prp5, a key regulator of early spliceosome assembly, and stimulates its ATPase activity thereby enhancing splicing and relaxing fidelity. High Hub1 levels enhance splicing efficiency but also cause missplicing by tolerating suboptimal splice sites and branchpoint sequences. Notably, Prp5 itself is regulated by a Hub1-dependent negative feedback loop. Since Hub1-mediated splicing activation induces cryptic splicing of Prp5, it also represses Prp5 protein levels and thus curbs excessive missplicing. Our findings indicate that Hub1 mediates enhanced, but error-prone splicing, a mechanism that is tightly controlled by a feedback loop of PRP5 cryptic splicing activation. [Display omitted] •Hub1 activates splicing in vitro•Hub1 acts as an ATPase stimulating co-factor of the DEAD-box helicase Prp5•Stimulation of spliceosomes by Hub1 activates cryptic splice sites•Overactivation of splicing is countered by a negative feedback loop Karaduman et al. show that Hub1, a ubiquitin-like protein, binds to and stimulates ATPase activity of the DEAD-box helicase Prp5, enhancing splicing efficiency, but at a cost of reduced fidelity.