Identification of a protein kinase activity in rabbit reticulocytes that phosphorylates the mRNA cap binding protein.
The 25 kDa mRNA cap binding protein can be purified in a partially phosphorylated state and the extent of its phosphorylation appears to be regulated during heat shock and mitosis in mammalian cells. We demonstrated that a nonabundant serine protein kinase activity exists in rabbit reticulocytes that phosphorylates the 25 kDa cap binding protein in both the free (eIF-4E) and complexed (eIF-4F) state. This kinase was not inhibited by the cAMP-dependent protein kinase inhibitory peptide IAAGRTGRRNAIHDILVAA, did not phosphorylate S6 ribosomal protein, did not phosphorylate p220 of eIF-4F as protein kinase C does and no other substrates for this kinase were apparent in reticulocyte ribosomal salt wash. The molecular identity of this kinase, the specific site(s) of eIF-4E that it phosphorylates and its in vivo regulatory role remain to be studied.
McMullin
E L
EL
Department of Medicine (Gastroenterology) and Cell Biology, Vanderbilt University School of Medicine, Nashville, TN 37232.
Haas
D W
DW
Abramson
R D
RD
Thach
R E
RE
Merrick
W C
WC
Hagedorn
C H
CH
D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism* / Q000494:pharmacology; D039561:Eukaryotic Initiation Factor-4E; D039562:Eukaryotic Initiation Factor-4F; D047908:Intracellular Signaling Peptides and Proteins; D010448:Peptide Initiation Factors / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D039381:RNA Cap-Binding Proteins; D012315:RNA Caps / Q000378:metabolism*; D011817:Rabbits; D012156:Reticulocytes / Q000201:enzymology*
D002352:Carrier Proteins; D039561:Eukaryotic Initiation Factor-4E; D039562:Eukaryotic Initiation Factor-4F; D047908:Intracellular Signaling Peptides and Proteins; D010448:Peptide Initiation Factors; D039381:RNA Cap-Binding Proteins; D012315:RNA Caps; C015482:protein kinase modulator; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases