Nuclear p26, a small heat shock/alpha-crystallin protein, and its relationship to stress resistance in Artemia franciscana embryos.

The role of the small heat shock/alpha-crystallin protein, p26, in transcription in Artemia franciscana embryos was examined using isolated nuclei, containing either control or elevated levels of p26, in transcription run-on assays. Heat shock or anoxia in vivo and acid pH in vitro were used to transfer p26 into nuclei. The results suggest that parameters other than, or in addition to, p26 are responsible for the reduced transcription rates observed and that decreases in pHi are involved. In vivo experiments indicate that RNA synthesis and, to a lesser extent, protein synthesis are downregulated in intact embryos recovering from heat shock and that the precursor pool is not limiting. Confocal microscopy confirmed that p26 moves into nuclei in response to heat shock and anoxia in vivo, and to low pH in vitro, and indicated that the nuclear distribution of p26 is similar under all three conditions. We present evidence that unstressed (control) embryos containing p26 in all their nuclei will not hatch, even under permissive conditions, and propose that they are unable to terminate diapause. Potential nuclear targets of p26 chaperone activity are discussed.