Define:Transport pathways. Details on sigma factors

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Define:Transport pathways. Details on sigma factors

Post by neon » Mon May 29, 2006 12:09 pm


Can someone please give me (or direct me to somewhere on the www containing ) a description of the phrase "transport pathway". (wikipedia no good in this instance!)

Secondly, I'd like to get a better understanding of sigma factor activity. If someone knows a good resource for this, please let me know. I have a general idea of the concept, but I need to clarify some points. Can you tell me if I am correct in thinking that:

If there is a [specific] promotor (call it promA) in an operon (operonA), then this requires (amongst other things) RNAP and a sigma factor - call this sfA. When sfA and RNAP bind and form the holoenzyme, the genes in operonA are transcribed. (ignore any activators/repressors for now).

OperonB contains promB etc...If only sfA is present, the genes in operonB will not be transcribed at all? And if sfB is present, only genes in operonB will be transcribed? Is is as clean-cut as this, or is there simply a bias in which operons are transcribed?

So in this situation, would the operons be completely separate? I.e. they would occupy completely separate stretches of the DNA?

If you can tell me whether my assumptions are correct, I would be most grateful.



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Post by weesper » Mon May 29, 2006 10:54 pm

Transport pathways usually refers to the transport of proteins from one domain in the cell to another; for example from the nucleus to the cytoplasm which is called nucleocytoplasmic transport, or from the endoplasmic reticulum to the Golgi apparatus. Most if not all of these types of transport are regulated by specific transport receptors that recognize signal sequences within in proteins (that is to say they recognize polypeptide sequences within proteins) that not only dock onto a recptor but also tell a receptor where this cargo should be headed.

For example the most common mutation in cystic fibrosis (deltaF508) is disease causing due to the fact that it disrupts proper routing of the protein and therefore it never reaches it final localisation the plasma membrane.

One another example might be nuclear transport; one group in the netherlands actually did interesting work on this showing that if you tweek the system you can artificially create novel peptide sequences that show much greater affinity for the most common nucleocytoplasmic transport receptor (see Engelsma et al Embo '04)

Lastly your assumptions about the sigma factor are correct; it potentiates prokaryotic transcription together with a transcription factor but as far as I know there is no specificity to this process

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