Possesses chaperone activity in vitro where it inhibits aggregation of citrate synthase. Homodimer. In the testis, forms a complex with p53 at 32.5 degrees Celsius which is scrotal temperature but not at 37 or 42 degrees Celsius. May translocate to the nucleus of germ cells after heat shock. Expressed at high levels in testis and at much lower levels in brain. In testis, expressed mainly in germ cells. Widespread in brain with highest expression in cerebellum and medulla oblongata. Also expressed in renal medulla of water-restricted animals. Expression is first detected in the testis 5 weeks after birth and coincides with the appearance of spermatozoa. In the brain, expression is first detected 3.5 days after birth. By heat shock. Belongs to the heat shock protein 70 family.