WW domain-binding protein 4 (WBP4; also known as formin-binding protein 21) is a component of the spliceosome, which is involved in pre-mRNA splicing. It contains a matrin-type zinc finger and two tandem WW domains. It interacts with the splicing factor SIPP1, and its binding and activation of pre-mRNA splicing depend on the WW domains []. This entry also includes zinc finger protein ZOP1 from Arabidopsis thaliana, which is also a pre-mRNA splicing factor that associates with several typical components of the splicing machinery and promotes Pol IV-dependent siRNA accumulation, DNA methylation, and transcriptional silencing [].
