The complex composed of CBC, SRRT and NCBP3 was shown to be mutually exclusive with PHAX and proposed to be part of an RNA-fate decision tree - similar decision forks between CBC, NELF-E or SRRT ( 5), and between SRRT, PHAX or ZC3H18 ( 8) have also been reported. Most recently, NCBP3 was shown to interact in vitro with both CBC (via NCBP1) and SRRT, separately and as a ternary complex ( 5). Previous reports described the association of NCBP3 with mRNPs to be splicing-linked, exon junction complex (EJC) independent and CBC-dependent ( 17) yet, NCBP3 has been grouped with the EJC and the TREX complex on the basis of protein-protein interaction studies ( 18–20). NCBP3 ( 5, 16), previously coined C17orf85 or ELG ( 17–19), was recently proposed to form an alternative CBC with NCBP1, capable of substituting for NCBP2 and suppressing the mRNA export defect caused by loss of NCBP2 ( 16). ![]() Within elongating (messenger) mRNPs, the CBC interacts with ALYREF in the ‘transcription/export’ (TREX) complex, promoting mRNA export ( 15). On snRNAs and a few independently transcribed snoRNAs, the CBCA complex may interact with PHAX, forming the CBCAP complex which stimulates nuclear export of snRNAs and the movement of snoRNAs to nucleoli ( 9, 12–14). CBCA can interact with ZC3H18, which may in turn recruit the nuclear exosome targeting (NEXT) complex or the poly(A) tail exosome targeting (PAXT) connection, directing bound RNAs to decay via the RNA exosome ( 10, 11). ARS2 (SRRT, Uniprot gene symbols preferentially used throughout) joins the CBC, forming the CBC-ARS2 (CBCA) complex, which influences the fate of multiple types of RNAs ( 8, 9).
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