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14 Expression and Function of Vertebrate hsp70 Genes

Richard I. Morimoto, Kim L Milarski


The eukaryotic genome encodes a large multigene family of hsp70-related proteins. In human cells, there are at least five distinct protein members of the hsp70 gene family (Fig. 1) that exhibit constitutive and inducible regulation and share biochemical and antigenic properties. The genes that encode many of these hsp70-related proteins have been cloned, and comparison of the corresponding nucleotide sequences has revealed a high degree of evolutionary conservation among members of the hsp70 family within a single species and between species (Moran et al. 1982; Lowe et al. 1983; Hunt and Morimoto 1985; Mues et al. 1986). For example, Escherichia coli DnaK and human hsp70 are 50% identical at the amino acid level (Bardwell and Craig 1984; Hunt and Morimoto 1985) whereas grp78, p72, and hsp70 are approximately 75–85% related. Under normal conditions of cell growth, different members of the hsp70 family are localized to particular cellular compartments and in response to physiological stress are redistributed to different intracellular locales. This feature is best represented by hsp70 and p72 which are typically found in the cytoplasm of cells in the G1 phase of the cell cycle and, following heat shock or other forms of stress, redistribute from the cytoplasm to the nucleus and nucleolus. Although the function of the hsp70-related proteins has not been firmly established, recent biochemical evidence suggests multiple roles for the hsp70-related proteins in the formation, maintenance, and disaggregation of complex multimeric structures and in protein folding (Chirico et al. 1988;...

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