Mutations in the parkin gene cause autosomal recessive, juvenile-onset 
parkinsonism. Parkin is an E3 ubiquitin ligase that mediates the ubiquitination 
of protein substrates. Disease-associated mutations cause a loss-of-function of 
parkin which may compromise the poly-ubiquitination and proteasomal degradation 
of specific protein substrates, potentially leading to their deleterious 
accumulation. Here, we identify the molecular chaperones, Hsp70 and Hsc70, as 
substrates for parkin. Parkin mediates the ubiquitination of Hsp70 both in vitro 
and in cultured cells. Parkin interacts with Hsp70 via its second RING finger 
domain and mutations in/near this domain compromise Hsp70 ubiquitination. 
Ubiquitination of Hsp70 fails to alter its steady-state levels or turnover, nor 
does it promote its proteasomal degradation. Consistent with this observation, 
Hsp70 levels remain unaltered in brains from parkin-deficient autosomal 
recessive, juvenile-onset parkinsonism subjects, whereas alternatively, Hsp70 
levels are elevated in the detergent-insoluble fraction of sporadic Parkinson's 
disease/dementia with Lewy bodies brains. Parkin mediates the multiple 
mono-ubiquitination of Hsp70/Hsc70 consistent with a degradation-independent 
role for this ubiquitin modification. Our observations support a novel 
functional relationship between parkin and Hsc/Hsp70 and support the notion that 
parkin is a multi-purpose E3 ubiquitin ligase capable of modifying proteins 
either via attachment of alternatively linked poly-ubiquitin chains or through 
multiple mono-ubiquitination to achieve alternate biological outcomes.