POLYMERIZATION OF 70-KDA HEAT-SHOCK PROTEIN BY YEAST DNAJ IN ATP

DnaK, the Escherichia coli hsp(70) protein, interacts with DnaJ, a pro tein cofactor that appears to be involved in presenting protein substr ates to DnaK. The yeast DnaJ homolog, YDJ1, has also been shown to int eract with yeast hsp70, although the function of this interaction is u nknown. In the present study, we investigated the interaction of YDJ1 with both yeast and bovine brain hsp70. We found that, in the presence of ATP, where hsp70 is normally monomeric, YDJ1 induced almost all of the yeast and bovine brain hsp70 to form large polymers, which are re adily sedimentable. These polymers were much larger than the dimers an d trimers of hsp70, which normally form in the presence of ADP. YDJ1 a ppeared to be acting catalytically since very little YDJ1 copolymerize d with the hsp70, and maximum polymerization occurred at low ratios of YDJ1 to hsp70. The polymerization required ATP and was completely rev ersed when ATP was replaced by ADP. These data suggest that, in the pr esence of ATP, YDJ1 may present one hsp70 to another just as under oth er conditions DnaJ is able to present protein substrates to DnaK.