The Hsp70 system is a highly conserved family of ubiquitous proteins found in all prokaryotes and in cellular compartments of eukaryotic organisms. Multiple members of this family are involved in protein folding and several other cellular functions. Some forms are constitutively expressed in cells, while others are only inducible by metabolic stress. Various stressors that induce Hsp70 include heat shock, hypoxia, UV irradiation, CdCl2 and arsenite. Basal levels of constitutive Hsp70 are found in major intracellular compartments and the inducible Hsp70s are predominantly cytoplasmic and nuclear in distribution. There are at least 11 genes for proteins of the human Hsp70 family, which code for a group of highly related proteins ranging from 66 to 78 kDa. The multiple members of this family vary with their basal expression levels and inducibility in response to different stressors. The Hsp70 chaperones have two major functional domains. The highly conserved NH2-terminal domain has ATPase activity and binds to ADP and ATP very tightly, and COOH-terminal binds to polypeptides. Hsp70 is known to bind preferentially to unfolded and partially folded proteins and prevent their aggregation or misfolding. The nomenclature of the different members of Hsp70 family is extensive and is based on cellular distribution and inducibility (refer to Appendix VI, page 24, for nomenclature of Hsp70 family members).<br/>Human HSP70B′ is a variant Hsp70 that is more basic than the major Hsp70 and has different stress-induction characteristics. There have been several reports of Hsp70 variants, but most of them are products of different postranslational modifications. HSP70B′ is a product of a separate gene which is devoid of introns similar to Hsp70. The HSP70B′ gene has 77% sequence identity to Hsp70 gene and 70% identity to Hsc70 cDNA with highest sequence divergence at the 3'- end. Promoter studies have shown HSP70B′ to be a unique member of the Hsp70 family. Unlike Hsp70 which shows basal levels of expression and is induced by heat and various stressors, HSP70B′ is strictly heat-inducible and shows no basal levels. One study reported the use of HSP70B′ as a target gene for studying single nucleotide?polymorphisms (SNP) in biopsy samples of human prostate cancer patients.