The human heat-shock protein family. Expression of a novel heat-inducible HSP70 (HSP70B′) and isolation of its cDNA and genomic DNA

The human heat-shock protein multigene family comprises several highly conserved proteins with structural and functional properties in common, but which vary in the extent of their inducibility in response to metabolic stress. We have isolated and characterized a novel human HSP70 cDNA, HSP70B′ cDNA, and its corresponding gene sequence. HSP70B′ cDNA hybrid-selected an mRNA encoding a more basic 70 kDa heat-shock protein that both the major stress-inducible HSP70 and constitutively expressed HSC70 heat-shock proteins, which in common with other heat-shock 70 kDa proteins bound ATP. The complete HSP70B′ gene was sequenced and, like the major inducible HSP70 gene, is devoid of introns. The HSP70B′ gene has 77% sequence similarity to the HSP70 gene and 70% similarity to HSC70 cDNA, with greatest sequence divergence towards the 3′-terminus. The HSP70B′ gene represents a functional gene, as indicated by Northern-blot analysis with specific oligonucleotides, hybrid-selected translation with a specific 3′ cDNA sequence and S1 nuclease protection experiments. In contrast with HSP70 mRNA, which is present at low concentrations in HeLa cells and readily induced by heat or CdCl2 treatment in both fibroblasts and HeLa cells, HSP70B′ mRNA was induced only at higher temperature and showed no basal expression. The differences in patterns of induction may be due to the special features of the promoter region of the HSP70B′ gene.