Characterization of high-molecular-mass heat shock proteins and 42 degrees C-specific heat shock proteins of murine cells.

There are two isoforms of high-molecular-mass heat shock protein (HMM-HSP), hsp105A and hsp105B, in murine FM3A cells. To characterize the HMM-HSPs, we here purified hsp105A and hsp105B, as well as 42 degrees C-specific HSPs that are specifically induced by continuous heating at 42 degrees C, from the cytoplasmic extracts of the FM3A cells heat-shocked at 42 degrees C for 8 h. Digestion of the hsp105A, hsp105B, and 42 degrees C-specific HSPs with lysyl endopeptidase generated 17,000-Da polypeptide fragments in common, and the N-terminal amino acid sequences of the fragments revealed a homology with those of the adenosine binding domain of hsp70 family proteins and actin. Thus, the two isoforms of hsp105 and the 42 degrees C-specific HSPs seemed to be very similar proteins having a ATP binding domain in common, and these HSPs may constitute a HMM-HSP family in murine cells.