CASEIN KINASE-I PHOSPHORYLATES THE 25-KDA MESSENGER-RNA CAP-BINDING PROTEIN

被引:32
作者
HAAS, DW
HAGEDORN, CH
机构
[1] VANDERBILT UNIV,MED CTR,SCH MED,DEPT MED,MCN C-2104,1161 21ST AVE S,NASHVILLE,TN 37232
[2] VANDERBILT UNIV,MED CTR,SCH MED,DEPT CELL BIOL,NASHVILLE,TN 37232
[3] VET ADM MED CTR,NASHVILLE,TN 37203
关键词
D O I
10.1016/0003-9861(91)90267-M
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
The 25-kDa mRNA cap-binding protein (eIF-4E) exists in both phosphorylated and dephosphorylated forms in eukaryotic cells. Phosphorylated eIF-4E appears to be preferentially associated with 48 S initiation complexes and with the 220-kDa subunit of eIF-4F. In addition, dephosphorylation of eIF-4E has been observed during heat shock and mitosis which are accompanied by decreased protein synthesis. However, the control of eIF-4E phosphorylation and its regulatory role remain poorly understood. Using eIF-4E as a substrate we have identified and purified from rabbit reticulocytes a protein kinase that phosphorylates eIF-4E in vitro. This enzyme phosphorylated eIF-4E on both serine and threonine residues with an apparent Km of 3.7 μm. The molecular mass of the enzyme and specificity for substrates other than eIF-4E suggested that this enzyme was a species of casein kinase I. This was confirmed by comparing the phosphopeptide map of the purified reticulocyte enzyme with that of rabbit skeletal muscle casein kinase I and by comparing phosphopeptide maps of eIF-4E phosphorylated in vitro by each enzyme. We conclude that casein kinase I phosphorylates eIF-4E in vitro and suggest that eIF-4E may be phosphorylated by casein kinase I in intact cells under some physiologic conditions. © 1991.
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页码:84 / 89
页数:6
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