Post-transcriptional regulation, why?

[Trond Erik Vee Aune]

Frank O. Fackelmayer wrote:

> Hi Trond,
> The more levels of regulation, the better.  
> PTR makes much sense. Consider mutations in a promoter that will
> increase or decrease transcription efficiency. Or viral infection with
> very strong transcription. Or the development of eggs, where lots of
> mRNA is made and stored for later use in the embryo.
> In those (and many more) cases it will be beneficial for the cell to
> have means to regulate translation rather than transcription. 
> 
> Hope this helps,


Yes, I do understand that it would be advantageous in these cases. But 
what about constituvely expressed E.coli proteins that the cell needs to 
have at a constant level? Why would evolution design sub-optimal 
translation efficiency of these? Why not just have a weak promotor and 
let translation be optimal? It seems to be a waste of energy to make 
mRNA which will be degraded before translated because of inefficient 
translation.

Trond Erik