NCBP3 is a nuclear cap-binding protein that forms an alternative cap-binding complex (CBC) with NCBP1, distinct from the conventional NCBP1/NCBP2 complex 1. Unlike the traditional CBC, the NCBP1/NCBP3 complex specifically binds mRNA rather than small nuclear RNAs (snRNAs), focusing its function on mRNA export and expression 1. NCBP3 functions as a regulatory hub that interacts with the Exon Junction Complex (EJC) and TREX machinery, competing with RNA degradation factors to promote nuclear export of polyadenylated RNAs and enhance expression of large multi-exonic transcripts 2. Under cellular stress such as viral infection, NCBP3 becomes critical for host defense and mRNA biogenesis, as the alternative CBC compensates when conventional pathways are compromised 1. In hypoxic cardiomyocytes, NCBP3 coordinates with METTL3 and eIF4A2 to enhance translation through m6A RNA methylation, functioning as a stress-responsive regulatory protein 3. Additionally, HIV-1 exploits NCBP3-containing CBC complexes by forming hypermethylated m7G caps to bypass mTOR-dependent translation control 4. Dysregulation of NCBP3 has been implicated in cancer progression, particularly in lung adenocarcinoma and glioma, where it promotes oncogenic gene expression programs 5 6.