On the cytosolic and perinuclear mortalin: an insight by heat shock.

We have identified, cloned and characterized a 66-kD protein from cytosolic fractions of mouse embryonic fibroblasts and named it mortalin (Wadhwa et al., J. Biol. Chem., 268, in press, 1993). Immortal fibroblasts were seen to harbor the same or very similar protein, however, localized in the perinuclear locale. The present report is on the differentially localized forms of p66 protein which are biochemically and structurally found to be widely the same. In fact, heat shock treatment could translocate the cytosolic form to the perinuclear position without any detectable biochemical modification. The observed phenomenon adds to the unique identity of mortalin in hsp70 family. Besides, it confers that only the minor differences in the protein probably enroute its differential cellular distribution and the associated function.