Co-chaperone which acts as a regulator of the Hsp70 chaperone machinery and may be involved in the processing of other ataxia-linked proteins. Predominantly cytoplasmic, a small portion is present in the nucleus and also shows a partial mitochondrial overlap with the mitochondrial marker Hsp60. Highly expressed in the central nervous system. Also found in skeletal muscle and at low levels in pancreas. The ubiquitin-like domain mediates interaction with the proteasome. The J domain is functional and is shown to stimulate E.coli dnaK ATPase activity. The disease is caused by variants affecting the gene represented in this entry. Truncated N-terminus. Truncated N-terminus.