Heat-inducible proteins that react with antibodies to chaperonin60 are localized in the nucleus of a fish cell line.

We report in the present paper that proteins which react with a polyclonal antibody (pAb) raised against the heat-shock protein chaperonin60 (cpn60) were revealed by indirect immunofluorescence in the nucleus of a fish (fathead minnow, Pimephales promelas) cell line after heat-shock. This immunoreactive cpn60 associated with the nucleolus and with discrete foci. An increased abundance of two nuclear proteins of approx. 57 and 42 kDa, present in approximately equal amounts, was detected by Western blotting using an anti-cpn60 pAb as a probe during the same time period that cpn60 was revealed in the nucleus. These proteins also reacted with a monoclonal antibody (mAb) against human cpn60 but did not react with an mAb against the cytoplasmic chaperonin, TCP1. The kinetics of translocation and pattern of nuclear localization of this immunoreactive cpn60 differed from that of stress70, another major family of heatshock proteins. We suggest that these nuclear immunoreactive cpn60 proteins are members of the cpn60 family and that they play a chaperone role in folding and assembly of proteins in the nucleus which is distinct from that of stress70.