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 Xenopus laevis 70 kDa heat shock cognate protein, hsc70.II. The protein coding region exhibited high identity with Xenopus hsc70.I (94%), suggesting that the two genes are the result of a genomic tetraploidization event which occurred in Xenopus over 30 million years ago. Also, hsc70.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 support the theory that the inducible and constitutive members of the hsp70 family diverged well before the emergence of amphibians. Also, hsc70.II contains a number of conserved elements including an ATP-binding domain, a nuclear localization signal and the carboxyl terminal motif, EEVD, which may have a role in chaperone function.