13 Regulation and Function of the HSP70 Multigene Family of Saccharomyces cerevisiae

Abstract

I. INTRODUCTION
hsp70 is the most abundant heat shock protein in many organisms. Escherichia coli contains a single HSP70 gene, dnaK, which is expressed at high levels during normal logarithmic growth and is induced upon a temperature upshift. In most, if not all, eukaryotes, the heat-inducible HSP70 gene is one of a number of related genes, referred to as the HSP70 multigene family (Ingolia et al. 1982; Watowich and Morimoto 1988; also see Morimoto and Milarski, this volume). The yeast Saccharomyces cerevisiae contains a family of at least nine HSP70-related genes. Eight of these genes, originally named YG100–YG107, have been renamed: YG100, YG102, YG106, and YG107 as SSA1, SSA2, SSA3, and SSA4, respectively; YG101 and YG103 as SSB1 and SSB2, respectively; YC104 as SSC1; YG105 as SSD1. These genes have been divided into the four subgroups A–D, as indicated by the third letter of the gene designation, on the basis of structural and functional criteria. The first two letters of the gene designation stand for Stress Seventy. Recently, another member of the yeast HSP70 family, KAR2, has been identified (Rose et al. 1989). The structural relationships of the first eight genes identified are shown in Figure 1. This tree is based on DNA sequence similarity and DNA:DNA hybridization data. The structural relationship among the genes is complex, with nucleotide identities ranging from 50% to 96%. In this paper, I discuss the expression of these genes and the genetic experiments carried out to attempt to elucidate the functional relationships...