MOLECULAR-CLONING OF A CDNA-ENCODING A XENOPUS-LAEVIS 70-KDA HEAT-SHOCK COGNATE PROTEIN, HSC70.II

We have isolated and sequenced a full-length cDNA clone encoding a Xen opus laevis 70 kDa heat shock cognate protein, hsc70.II. The protein c oding region exhibited high identity with Xenopus hsc70.I (94%), sugge sting that the two genes are the result of a genomic tetraploidization event which occurred in Xenopus over 30 million years ago. Also, hsc7 0.II displayed a high level of identity with mammalian hsc70. However, the identity of Xenopus hsc70.II cDNA with Xenopus hsp70 was only 82% . At the carboxyl end of the hsc70.II protein, the identity with hsc70 .I was 85%, while the identity for hsp70 was only 58%, These data supp ort the theory that the inducible and constitutive members of the hsp7 0 family diverged well before the emergence of amphibians. Also, hsc70 .II contains a number of conserved elements including an ATP-binding d omain, a nuclear localization signal and the carboxyl terminal motif, EEVD, which may have a role in chaperone function.