The function of C9orf78 (chromosome 9 open reading frame 78, Ensembl gene identifier ENSG00000136819) is as follows. Plays a role in pre-mRNA splicing by promoting usage of the upstream 3'-splice site at alternative NAGNAG splice sites; these are sites featuring alternative acceptor motifs separated by only a few nucleotides (PubMed:35241646). May also modulate exon inclusion events (PubMed:35241646). Plays a role in spliceosomal remodeling by displacing WBP4 from SNRNP200 and may act to inhibit SNRNP200 helicase activity (PubMed:35241646). Binds U5 snRNA (PubMed:35241646). Required for proper chromosome segregation (PubMed:35167828). Not required for splicing of shelterin components (PubMed:35167828). .