what proteins turn on operons for RNA?

Answer 1

I know about the lac operon.

"Lactose operon repressor (lac repressor) is a protein that regulates lactose consumption by E.coli bacteria. The lac repressor binds DNA in the absence of lactose, and prevents RNA polymerase from beginning the transcription."

Hope this helped some.

Answer 2

An operator is a segment of DNA which regulates the activity of the structural genes of the operon that it is linked to, by interacting with a specific repressor or activator. It is a
regulatory sequence for shutting a gene down or turning it "on".

Control of operon genes is a type of gene regulation that enables organisms to regulate the expression of various genes depending on environmental conditions. Operon regulation can be either negative or positive. Negative regulation involves the binding of a repressor to the operator to prevent transcription.

In negative inducible operons, a regulatory repressor protein is normally bound to the operator and it prevents the transcription of the genes on the operon. If an inducer molecule is present, it binds to repressor and changes its conformation so that it is unable to bind to the operator. This allows for the transcription of the genes on the operator.

In negative repressible operons, transcription of the genes on the operon normally takes place. Repressor proteins are produced by a regulator gene but they are unable to bind to the operator in their normal conformation. However certain molecules called corepressors can bind to the repressor protein and change its conformation so that it can bind to the operator. The activated repressor protein binds to the operator and prevents transcription.

Operons can also be positively controlled. With positive control, an activator protein stimulates transcription by binding to DNA (usually at a site other than the operator).

In positive inducible operons, activator proteins are normally unable to bind to the pertinent DNA. However, certain substrate molecules can bind to the activator proteins and change their conformations so that they can bind to the DNA and enable transcription to take place.

In positive repressible operons, the activator proteins are normally bound to the pertinent DNA segment. However, certain molecules can bind to the activator and prevent it from binding to DNA. This prevents transcription.

Example
The lac operon :

The lac operon is an operon required for the transport and metabolism of lactose in Escherichia coli and some other enteric bacteria. It consists of three adjacent structural genes, a promoter, a terminator, and an operator. The lac operon is regulated by several factors including the availability of glucose and of lactose.
In the absence of lactose, the repressor protein encoded by the I gene binds to the lac operator and prevents transcription. Binding of lactose (and its relatives) to the repressor causes it to leave the operator. This enables RNA polymerase to transcribe the three structural genes of the operon. The single mRNA molecule that results is then translated into the three proteins.

Answer 3

you can look here..............http://boinc.bakerlab.org/rosetta/