The J‐protein family: modulating protein assembly, disassembly and translocation

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Abstract
DnaJ is a molecular chaperone and the prototypical member of the J‐protein family. J proteins are defined by the presence of a J domain that can regulate the activity of 70‐kDa heat‐shock proteins. Sequence analysis on the genome of Saccharomyces cerevisiae has revealed 22 proteins that establish four distinguishing structural features of the J domain: predicted helicity in segments I'IV, precisely placed interhelical contact residues, a lysine‐rich surface on helix II and placement of the diagnostic sequence HPD between the predicted helices II and III. We suggest that this definition of the J‐protein family could be used for other genome‐wide studies. In addition, three J‐like proteins were identified in yeast that contain regions closely resembling a J domain, but in which the HPD motif is non‐conservatively replaced. We suggest that J‐like proteins might function to regulate the activity of bona fide J proteins during protein translocation, assembly and disassembly.