ZIPPAY, M.L.*; HOFMANN, G.E.; University of California, Santa Barbara; University of California, Santa Barbara: DNA binding activity of the transcription factor, heat-shock factor 1, in the intertidal mussel Mytilus californianus during ecologically relevant fluctuations in body temperature

In order to examine plasticity of heat-shock protein (Hsp) gene expression, we measured the DNA binding activity of heat-shock factor 1 (HSF1), the transcriptional factor that activates heat stress-inducible Hsp genes, in the intertidal mussel, Mytilus californianus, during low tide emersion. In the intertidal mussel beds, mussels were exposed for an entire low tide series, where body temperatures increased from the temperature of ambient seawater (~10 °C) to nearly 30 °C in a 6-8 hour period. Just prior to immersion, mussels were collected and transferred to a seawater tank at 10 °C (to mimic the return of the tide) to begin an 18 h �recovery� phase. Mussels (n=3) were then sampled at time intervals during the recovery phase; gill tissue was dissected and frozen on dry ice for analysis. In order to measure the transactivation of Hsp genes during the recovery phase, we measured the DNA binding activity of HSF1 in gill using an electromobility shift assay (EMSA). Results showed a cyclic pattern of HSF1 activity where DNA binding activity was high early in the recovery phase, declined after 6-8 h, and remained low until the end of the recovery sampling period. These data indicate that Hsp genes are transcribed, and Hsps are synthesized, well after the tide has returned and mussel body temperatures have declined to 10 °C. Overall, the results of this study suggest that molecular chaperone synthesis and protein homeostasis activities were continuing during the recovery phase for several hours following the stressful temperature event that occurred during low tide. Supported by NSF grant IBN 0096100 to GEH.