Phosphorylation of plant eukaryotic initiation factor-2 by the plant-encoded double-stranded RNA-dependent protein kinase, pPKR, and inhibition of protein synthesis in vitro.
Regulation of protein synthesis by eukaryotic initiation factor-2alpha (eIF-2alpha) phosphorylation is a highly conserved phenomenon in eukaryotes that occurs in response to various stress conditions. Protein kinases capable of phosphorylating eIF-2alpha have been characterized from mammals and yeast. However, the phenomenon of eIF2-alpha-mediated regulation of protein synthesis and the presence of an eIF-2alpha kinase has not been demonstrated in higher plants. We show that plant eIF-2alpha (peIF-2alpha) and mammalian eIF-2alpha (meIF-2alpha) are phosphorylated similarly by both the double-stranded RNA-binding kinase, pPKR, present in plant ribosome salt wash fractions and the meIF-2alpha kinase, PKR. By several criteria, phosphorylation of peIF-2alpha is directly correlated with pPKR protein and autophosphorylation levels. Significantly, pPKR is capable of specifically phosphorylating Ser51 in a synthetic eIF-2alpha peptide, a key characteristic of the eIF-2alpha kinase family. Taken together, these data support the concept that pPKR is a member of the eIF-2alpha kinase family. In addition, the inhibition of brome mosaic virus RNA in vitro translation in wheat germ lysates by the addition of double-stranded RNA, phosphorylated peIF-2alpha, meIF-2alpha, or activated human PKR suggests that plant protein synthesis may be regulated via phosphorylation of eIF-2alpha.
Langland
J O
JO
Department of Plant, Soil, and Insect Sciences, University of Wyoming, Laramie, Wyoming 82071, USA.
Langland
L A
LA
Browning
K S
KS
Roth
D A
DA
D000595:Amino Acid Sequence; D000818:Animals; D002846:Chromatography, Affinity; D015852:Eukaryotic Initiation Factor-2 / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D001467:Hordeum / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008322:Mammals; D010750:Phosphoproteins / Q000302:isolation & purification / Q000378:metabolism; D010766:Phosphorylation; D014176:Protein Biosynthesis; D017346:Protein Serine-Threonine Kinases / Q000302:isolation & purification / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism; D012694:Serine; D013379:Substrate Specificity; D014908:Triticum; D019892:eIF-2 Kinase
D015852:Eukaryotic Initiation Factor-2; D010750:Phosphoproteins; D012694:Serine; D017346:Protein Serine-Threonine Kinases; D019892:eIF-2 Kinase