CSTF77

CstF-77, or the 77 kilodalton subunit of the cleavage stimulation factor (CstF), is a core component of the CstF complex that participates in the 3' end processing of pre-mRNA in eukaryotic cells. It functions as part of a trimeric complex that typically includes CstF-64 and CstF-50, coordinating with other 3' end processing factors to promote cleavage and subsequent polyadenylation of pre-mRNA.

Within the CstF complex, CstF-77 acts largely as a scaffolding subunit that facilitates assembly and protein–protein interactions. It helps bridge CstF to other components of the cleavage and polyadenylation machinery, including the cleavage stimulation factor CPSF, enabling efficient recognition of the downstream RNA elements and proper positioning of the cleavage site. While CstF-77’s direct RNA-binding role is limited, its interactions are essential for stable complex formation and activity.

CstF-77 is conserved across eukaryotes and is predominantly localized in the nucleus, where transcription and pre-mRNA processing occur. Regulation of CstF-77 function can influence polyadenylation site choice and mRNA maturation, impacting alternative polyadenylation patterns and gene expression. Dysfunction or altered expression of CstF-77 can contribute to shifts in transcript isoforms and related cellular phenotypes.

In summary, CstF-77 is a key scaffolding subunit of the CstF complex that supports the coupling of transcription termination to 3' end processing by facilitating interactions among processing factors and promoting cleavage and polyadenylation of pre-mRNA.