Characterization of an hsp70 related clone encoding a 33 kDa protein with homology to a protein which associates with polysomes.

Characterization of an hsp70 related Chinese hamster cDNA clone revealed that it encodes a 33 kDa protein with homology to a mouse ribosomal component p40 which associates with polysomes (Auth and Brawerman (1992) Proc. Natl. Acad. Sci. USA 89, 4368). The predicted amino acid sequence of this cDNA which differs by only two residues from p40, shares significant similarity with various members of the hsp70 family. Sequence analysis revealed a 29% identity between the N-terminal region (residues 1 to 120) of the 33 kDa protein and the ATP binding domain of the Chinese hamster hsc70, but no significant sequence similarity was found between the remaining C-terminal regions of the 33 kDa polypeptide and the hsc70 protein. The N-terminal region of the 33 kDa protein lacks the typical consensus motif for ATP binding, suggesting that the N-terminal domain of the 33 kDa protein may not be involved in ATP binding. In the light of the fact that this 33 kDa protein is a ribosomal component, we speculate that the N-terminal domain may interact with structures containing nucleotides such as RNA.