Protein kinases that phosphorylate and regulate eIF2B

点击翻译按钮获取中文摘要

Interactions between proteins modulate essential cell functions ensuring that cells can grow and perform their tasks. Each protein is like a piece in a machine, each must be in the correct place and act at the correct time with all the other parts for the machine to function properly. But unlike most machines and their parts, proteins are continually renewed, move and can be modified to alter their function and/or location. Many proteins act together as parts of protein complexes with a common function. One group of proteins relevant to this proposal is required make (or synthesize) all new proteins in the cell. These are called protein synthesis factors. By increasing or reducing the activity of some of the protein synthesis factors cells can control exactly what new proteins are made at any one time. One common way to alter the activity of proteins is by the addition of phosphate groups to specific places on the surface of the protein. This is called phosphorylation and is performed by a class of proteins called protein kinases. Each kinase responds to specific signals that tell it when to act. We have found that one key protein synthesis factor called eIF2B is phosphorylated at multiple sites, and that this phosphorylation enhances the activity of eIF2B. We are proposing here a series of experiments designed to discover which of the protein kinases present in the cell is responsible for each phosphorylation and to discover how each modification alters eIF2B function in the cell. In yeast cells there are 122 protein kinases. Using modern technologies we will be able to assess the role each one plays in control of eIF2B simultaneously. eIF2B function is also inhibited by phosphorylation of a second protein synthesis factor called eIF2. eIF2 is known to be phosphorylated at a single site called ser51 in response to diverse cell stresses. We have already determined that three of the five parts (or subunits) of eIF2B are all needed to correctly detect whether or not eIF2 is phosphorylated at this key regulatory site. But how exactly do these three subunits of eIF2B act together to do this? In a second series of experiments we propose to use a combination of genetic and biochemistry tools to address this question. This work will provide important detailed molecular information on how the activities of these essential proteins are controlled by phosphorylation.