Calf thymus Hsc70 and Hsc40 can substitute for DnaK and DnaJ function in protein renaturation but not in bacteriophage DNA replication

Calf thymus (et) Hsc70 has been shown previously to reactivate heat-inactiv ated prokaryotic and eukaryotic enzymes, while DnaK was able to reactivate solely prokaryotic enzymes. Here, we report on isolation from calf thymus o f a DnaJ homolog, ctHsc40, and on testing of its cooperative function in th ree different assays: (i) reactivation of heat-inactivated DNA polymerases, (ii) stimulation of the ATPase activity of ctHsc70 chaperone, and (iii) re plication of bacteriophage lambda DNA. Surprisingly, ctHsc70/ctHsc40 chaper ones were found to reactivate the denatured prokaryotic and eukaryotic enzy mes but not to promote bacteriophage lambda DNA replication, suggesting spe cies specificity in DNA replication. (C) 2001 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.