Signal Transduction Mechanisms 



A fundamental issue in interpreting molecular signals on short 

 time scales is how environmental cues are sensed, what the 

 mechanisms are for signal transduction, and how these signals are 

 extended to elicit gene expression. The physiological literature 

 is rife with descriptions of how a variety of cues, including 

 light, temperature, pH, salt, pressure, nutrient availability, and 

 dissolved organic compounds, affect the growth, behavior, and 

 reproductive responses in myriad organisms. Signal transduction 

 mechanisms are found in procaryotes, as well as in higher 

 organisms. In the evolution of transduction mechanisms, common 

 genetic switches and switching mechanisms are likely to have been 

 conserved. Signal transduction mechanisms have been isolated and 

 described in one or two model systems; however, it is unclear how 

 far these models can be extrapolated. Therefore, a second aspect 

 of using a diagnostic approach to interpreting how organisms are 

 affected by the environment, requires a comparison of common 

 regulatory and signal transduction motifs at the molecular level. 



Some key questions on signal transduction mechanisms that were 

 identified are the following: 



• Are the sequences or motifs in flanking regions on genes 

 that code for stress-induced proteins conserved in a wide 

 variety of organisms? 



• How are transcriptional elements, or factors, activated 

 by external chemical or physical signals? 



• How are the activation processes reversed; i.e., how does 

 environmental regulation of genes fundamentally differ 

 from cellular differentiation? How are these two 

 processes similar? 



• How varied are the environmental sensing systems in 

 natural ecosystems? 



Energetics 



Although the external physical and chemical environment 

 controls many ecosystem functions, as was described briefly in the 

 section on limiting factors, inherent metabolic processes also play 



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