Intracellular translation initiation factor levels in Saccharomyces cerevisiae and their role in cap-complex function

被引:107
作者
von der Haar, T [1 ]
McCarthy, JEG [1 ]
机构
[1] Univ Manchester, Dept Biomol Sci, Posttranscript Control Grp, Manchester M60 1QD, Lancs, England
关键词
D O I
10.1046/j.1365-2958.2002.03172.x
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
Knowledge of the balance of activities of eukaryotic initiation factors (eIFs) is critical to our understanding of the mechanisms underlying translational control. We have therefore estimated the intracellular levels of 11 eIFs in logarithmically growing cells of Saccharomyces cerevisiae using polyclonal antibodies raised in rabbits against recombinant proteins. Those factors involved in 43S complex formation occur at levels comparable (i.e. within a 0.5- to 2.0-fold range) to those published for ribosomes. In contrast, the subunits of the cap-binding complex eIF4F showed considerable variation in their abundance. The helicase eIF4A was the most abundant eIF of the yeast cell, followed by eIF4E at multiple copies per ribosome, and eIF4B at approximately one copy per ribosome. The adaptor protein eIF4G was the least abundant of the eIF4 factors, with a copy number per cell that is substoichiometric to the ribosome and similar to the abundance of mRNA. The observed excess of eIF4E over its functional partner eIF4G is not strictly required during exponential growth: at eIF4E levels artificially reduced to 30% of those in wild-type yeast, growth rates and the capacity for general protein synthesis are only minimally affected. This demonstrates that eIF4E does not exercise a higher level of rate control over translation than other eIFs. However, other features of the yeast life cycle, such as the control of cell size, are more sensitive to changes in eIF4E abundance. Overall, these data constitute an important basis for developing a quantitative model of the workings of the eukaryotic translation apparatus.
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页码:531 / 544
页数:14
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