In yeast, the replication helicase MCM2-7 (minichromosome maintenance) complex enters the nucleus as an inactive double hexamer during mitosis.

TLS Online TPP Program

#Id: 6311

#Unit 3. Fundamental Processes

he consequences of arrest can be catastrophic if the gene being transcribed is essential as no product will be made by the arrested polymerase, and that same enzyme will cause a roadblock to other polymerases attempting to transcribe the same gene.The cell has machinery that removes the arrested polymerase and at the same time recruits repair enzymes (in particular, the endonuclease Uvr(A)BC); the repair that follows is called transcription-coupled repair. Both polymerase removal and repair enzyme recruitment are performed by a single protein called TRCF.

TLS Online TPP Program

#Id: 6312

#Unit 3. Fundamental Processes

TRCF has an ATPase activity. 

Base-pairing of something to the transcript to destabilize RNA-DNA hybrid

Causes hairpin to form

Causing the transcription to pause

Causes a string of U’s to be incorporated just downstream of hairpin

TLS Online TPP Program

#Id: 6313

#Unit 3. Fundamental Processes

Sequence of a Rho-independent terminator

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.