Mutually exclusive interactions drive handover of mRNA from export adaptors to TAP.
Adaptor proteins stimulate the nuclear export of mRNA, but their mechanism of action remains unclear. Here, we show that REF/ALY binds mRNA; but upon formation of a ternary complex with TAP the RNA is transferred from REF to TAP, and overexpression of TAP displaces REF from mRNA in vivo. RNA is also handed over from two other adaptors, 9G8 and SRp20 to TAP upon formation of a ternary complex. Interestingly, the RNA-binding affinity of TAP is enhanced 4-fold in vitro once it is complexed with REF. 9G8 and SRp20 also enhance the TAP RNA-binding activity in vitro. Consistent with a model in which TAP directly binds mRNA handed over from adaptors during export, we show that TAP binds mRNA in vivo by an arginine-rich motif in its N-terminal domain. The importance of direct TAP-mRNA interactions is confirmed by the observation that a mutant form of TAP that fails to bind mRNA but retains the ability to bind REF does not function in mRNA export.
Hautbergue
Guillaume M
GM
Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, United Kingdom.
Hung
Ming-Lung
ML
Golovanov
Alexander P
AP
Lian
Lu-Yun
LY
Wilson
Stuart A
SA
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D053487:DEAD-box RNA Helicases / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D029543:Nucleocytoplasmic Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D034443:RNA Transport; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D029543:Nucleocytoplasmic Transport Proteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D053487:DEAD-box RNA Helicases