Extramitochondrial localization of mortalin/mthsp70/PBP74/GRP75

Subcellular fractionation and immunofluorescence microscopy were used to id entify the specific sites of intracellular residence of mortalin, also call ed a mitochondrial homologue of the hsp70 family, in immortal human cell Li nes previously assigned to four distinct complementation groups (A-D) for i ndefinite cell division. In addition to the mitochondria it was seen in the endoplasmic reticulum (ER) fractions of all the cell Lines analyzed. Inter estingly, three of the group A cells lines (EJ, GM639, and HT1080), in addi tion to the mitochondria and ER, exhibited cytosolically (extra-organelle) localized pool of mortalin. These findings demonstrate that mortalin is not present exclusively in mitochondria Its residence in different organelles may be the basis of differential distribution observed previously in differ ent human cell lines. (C) 2000 Academic Press.