Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: July 10, 2002
Publication Date: N/A
Technical Abstract: The Stress70 proteins do not function independently, but rather in association with cohort or co-chaperone proteins. The functional association of these components is often referred to as the Stress70 chaperone "machine." The archetype of the Stress70 chaperone machine has been defined in Escherichia coli, and consists of the products of dnaK (Stress70), dnaJ, and grpE. DnaK is the central, ATP-dependent component of the machine, and functions as a chaperone in association with GrpE, a nucleotide exchange factor, and DnaJ, an activating protein that stimulates the rate of hydrolysis of DnaK-bound ATP. It was subsequently discovered, using both biochemical and genetic methods, that DnaJ interacts directly with DnaK and GrpE, comprising a multi-component molecular chaperone machine. In addition, it has been demonstrated that DnaJ can act as a chaperone independently. The characteristic feature of DnaJ is the presence of the J-domain, a conserved approximately 75 amino acid sequence that forms multiple alpha-helices. The invariant tripeptide, HPD, which is both characteristic of and absolutely essential for the biological function of J-domains, is located between helices II and III. The only known role for the J-domain is interaction with the Stress70 component of the molecular chaperone machine. The Arabidopsis thaliana genome includes an unexpectedly large and diverse family of J-domain proteins. The results from in-silico analyses suggest that there are species present in all subcellular compartments. Included are seven species predicted to be localized within the mitochondrial matrix, and at least three associated with the mitochondrial membranes. Cell fractionation, in vitro transcription/translation/import, and laser confocal microscopy of fluorescent protein fusions, are being used to test the in silico predictions.