Identification of novel phosphorylation sites in the beta-subunit of translation initiation factor eIF-2.
Initiation factor eIF-2 (a trimer of subunits alpha, beta and gamma) attaches the initiator Met-tRNA to the ribosome during the initiation of translation in eukaryotic cells. Both the alpha and beta subunits can be phosphorylated although the sites in the beta-subunit have not previously been fully identified. Here we identify the sites at which eIF-2 beta is phosphorylated in vitro by three well-characterised protein kinases, casein kinase-2 (which phosphorylates serine residues-2 and -67), protein kinase C (serine-13) and cAMP-dependent protein kinase (serine-218). This constitutes an essential prerequisite for studying the phosphorylation of eIF-2 beta in vivo. Indeed, we present evidence that at least one of these sites (serine-67) is phosphorylated in reticulocytes. The major kinase activity against eIF-2 beta in reticulocyte lysates appears in CK-2 and protein phosphatase-2A is the principal enzyme responsible for dephosphorylation of eIF-2 beta phosphorylated by this kinase.
Welsh
G I
GI
Department of Biochemistry, School of Medical Sciences, University of Bristol, United Kingdom.
Price
N T
NT
Bladergroen
B A
BA
Bloomberg
G
G
Proud
C G
CG
D000595:Amino Acid Sequence; D000818:Animals; D003402:Creatine Kinase / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism*; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D010449:Peptide Mapping; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D010769:Phosphothreonine / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D011817:Rabbits
D015852:Eukaryotic Initiation Factor-2; D010446:Peptide Fragments; D010769:Phosphothreonine; D010768:Phosphoserine; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D003402:Creatine Kinase