* Author for correspondence Summary

Exposure of HeLa S3 cells to high hydrostatic pressure (6.89 xlO3 to 6.89xl04kPa: 1000 to lOOOOlbfin"2) reduced core and HI histone mRNA levels as determined by hybridization to specific histone DNA probes. At 4.14xl04kPa for lOmin core histone and HI histone mRNA levels were reduced 32-38 % and 58%, respectively. At 30min post-decompression core mRNA levels returned to atmos-pheric control levels while HI histone mRNA levels continued to be suppressed. Levels of macromolecu-lar synthesis were monitored under hydrostatic pressure with radioactive precursors of RNA, DNA and protein. Macromolecular synthesis was shown to be suppressed in a dose-dependent manner with increasing magnitude and duration of pressure. To determine the influence of pressure on histone mRNA stability, actinomycin D (lO/igml"1) was used to block RNA synthesis. Relative amounts of H4 and HI mRNA were determined at atmospheric pressure and following treatment with actinomycin D (10/igmT1), pressure (4.14xl04kPa) and a combi-nation of pressure and actinomycin D. This study shows that a synthesis component and a stability component are involved in the pressure-induced reduction of core histone mRNA. At 4.14x 104 kPa for 15min, there was a 42 % reduction in core histone mRNA of which approximately one third was due a suppression of transcription and two thirds to a loss of mRNA stability. The pressure-induced reduction in histone mRNA is attributed to the instability of endogenous histone mRNA and a reduction in transcription/processing of new histone mRNA. Key words: hydrostatic pressure, histone, mRN