Phosphorylation states of translational initiation factors affect mRNA cap binding in wheat.
Phosphorylation of eukaryotic translational initiation factors (eIFs) has been shown to be an important means of regulating protein synthesis. Plant initiation factors undergo phosphorylation/dephosphorylation under a variety of stress and growth conditions. We have shown that recombinant wheat cap-binding protein, eIF(iso)4E, produced from E. coli can be phosphorylated in vitro. Phosphorylation of eIF(iso)4E has effects on m(7)G cap-binding affinity similar to those of phosphorylation of mammalian eIF4E even though eIF(iso)4E lacks an amino acid that can be phosphorylated at the residue corresponding to Ser-209, the phosphorylation site in mammalian eIF4E. The cap-binding affinity was reduced 1.2-2.6-fold when eIF(iso)4E was phosphorylated. The in vitro phosphorylation site for wheat eIF(iso)4E was identified as Ser-207. Addition of eIF(iso)4G and eIF4B that had also been phosphorylated in vitro further reduced cap-binding affinity. Temperature-dependent studies showed that DeltaH(degrees) was favorable for cap binding regardless of the phosphorylation state of the initiation factors. The entropy, however, was unfavorable (negative) except when eIF(iso)4E was phosphorylated and interacting with eIF(iso)4G. Phosphorylation may modulate not only cap-binding activity, but other functions of eukaryotic initiation factors as well.
Khan
Mateen A
MA
Department of Chemistry, Hunter College and the Graduate Center of the City University of New York, New York 10021, USA.
Goss
Dixie J
DJ
D039561:Eukaryotic Initiation Factor-4E / Q000378:metabolism; D039603:Eukaryotic Initiation Factor-4G / Q000378:metabolism; D039642:Eukaryotic Initiation Factors / Q000378:metabolism; D010448:Peptide Initiation Factors / Q000378:metabolism*; D010750:Phosphoproteins / Q000502:physiology; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D012314:RNA Cap Analogs / Q000378:metabolism; D012315:RNA Caps / Q000378:metabolism*; D012333:RNA, Messenger; D011994:Recombinant Proteins; D013816:Thermodynamics; D014908:Triticum / Q000235:genetics
D039561:Eukaryotic Initiation Factor-4E; D039603:Eukaryotic Initiation Factor-4G; D039642:Eukaryotic Initiation Factors; D010448:Peptide Initiation Factors; D010750:Phosphoproteins; D012314:RNA Cap Analogs; D012315:RNA Caps; D012333:RNA, Messenger; D011994:Recombinant Proteins; C031799:eIF-4B; C017516:7-methylguanosine triphosphate