fluidity (DeLong and Yayanos, 1985; Cossins and Macdonald, 1986) . 

 Deep-sea eubacteria and archaebacteria also elevate the steady- 

 state production of specific proteins as a function of growth 

 pressure in a barometer-like fashion. In one abyssal bacterium 

 which has been studied in detail, a gene encoding an outer membrane 

 protein is transcriptionally regulated by elevated hydrostatic 

 pressure (Bartlett et al., 1989) . This protein appears to function 

 as a generalized diffusion channel for nutrient uptake. 



The structure-function rules which govern the molecular 

 changes conferring pressure adaptation in proteins have not been 

 determined. Future research will focus on the processes by which 

 deep-sea organisms sense and respond to variations in pressure, the 

 regulation of specific genes by pressure, and the function and 

 conservation of those gene products which are essential for 

 pressure adaptation. 



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