In global genome repair (GG-NER), the XPC protein detects the damage and initiates the repair pathway. XPC can recognize damage anywhere in the genome. In mammals, XPC is a component of a lesion-sensing complex that also includes the proteins HR23B and centrin2.

TLS Online TPP Program

#Id: 6314

#Unit 3. Fundamental Processes

There are 1100 sequences terminators in the E. coli genome

Intrinsic terminators include palindromic regions that form hairpins varying in length from 7 to 20 bp. The stem-loop structure includes a G-C–rich region and is followed by a run of 7U residues.

TLS Online TPP Program

#Id: 6315

#Unit 3. Fundamental Processes

Model of Intrinsic Termination

Bacterial terminators act by:

TLS Online TPP Program

#Id: 6316

#Unit 3. Fundamental Processes

Readthrough transcripts refer to the fraction of transcripts that are not stopped by the terminator.  Furthermore, the termination event can be prevented by specific ancillary factors that interact with RNA and/or RNA polymerase, a situation referred to as antitermination.

TLS Online TPP Program

#Id: 6317

#Unit 3. Fundamental Processes

TLS Online TPP Program

#Id: 6318

#Unit 3. Fundamental Processes

Rho binds to a sequence within the transcript upstream of the site of termination. This sequence is called a rut site (an acronym for rho utilization). 

The rho factor then tracks along the RNA until it catches up to RNA polymerase. When the RNA polymerase reaches the termination site, rho first freezes the structure of the polymerase and then invades the exit channel to destabilize the enzyme, causing it to release the RNA.

TLS Online TPP Program

#Id: 6319

#Unit 3. Fundamental Processes

A rut site has a sequence rich in C and poor in G preceding the actual site(s) of termination. The sequence corresponds to the 3’ end of the RNA.