Myosin II

Two heads and assembles into bipolar filaments

Small and non-processive

Function- Contraction

#Id: 2420

#Unit 3. Fundamental Processes

Intrinsic terminators—that is, those that do not require auxiliary rho factor (r), as described shortly—require a GC–rich hairpin to form in the secondary structure of the RNA being transcribed.

#Id: 2421

#Unit 3. Fundamental Processes

Rho-dependent terminators are defined by the need for addition of rho factor in vitro, and mutations show that the factor is involved in termination in vivo.

#Id: 2422

#Unit 3. Fundamental Processes

Point mutations that reduce termination efficiency usually occur within the stem region of the hairpin, replacing GC base pairs with weaker AT base pairs, or in the U-rich sequence, supporting the importance of these sequences in the mechanism of termination.

#Id: 2423

#Unit 3. Fundamental Processes

Readthrough transcripts refer to the fraction of transcripts that are not stopped by the terminator. (Readthrough is the same term used in translation to describe a ribosome’s suppression of termination codons.) 

#Id: 2424

#Unit 3. Fundamental Processes

the termination event can be prevented by specific ancillary factors that interact with RNA and/or RNA polymerase, a situation referred to as antitermination.

#Id: 2425

#Unit 3. Fundamental Processes

There are other parallels between initiation and termination. Both require breaking of hydrogen bonds (initial melting of DNA at initiation and RNA–DNA dissociation at termination), and both can utilize additional proteins (sigma factors, activators, repressors, and rho factor) that interact with the core enzyme.