Isolation and characterization of SSE1 and SSE2, new members of the yeast HSP70 multigene family.

Two new members of the Saccharomyces cerevisiae heat-shock protein 70 multigene (HSP70) family were isolated from a yeast expression library using antisera made against a yeast calmodulin-binding fraction. They are designated as SSE1 and SSE2, because their predicted amino acid (aa) sequences are highly homologous to each other (76% identical), and share homology with known members of the yeast HSP70 multigene family, but their homologies (13 to 28% identity) are not high enough to place them in known subfamilies. SSE1 and SSE2 are thought to encode polypeptides of 693 aa with calculated M(r)'s of 77,408 and 77,619, respectively. The SSE1 mRNAs were moderately abundant during steady-state growth at 23 degrees C, and increased a few-fold upon upshift to 37 degrees C. SSE2 mRNAs were present at low level during steady-state growth at 23 degrees C, and greatly increased upon upshift to 37 degrees C. Disruption of SSE1 results in slow-growing cells at any temperature. No phenotypic effects of the mutation in SSE2 were detected, and the growth property of the sse1sse2 double mutant was the same as that of the sse1 single mutant.