Rhoindependent

Rho-independent transcription termination, also known as intrinsic termination, is a bacterial mechanism that ends transcription without the involvement of the Rho factor.

Typical intrinsic terminators consist of a GC-rich palindromic inverted repeat that forms a stable hairpin, or stem-loop, in the nascent RNA, followed by a short stretch of uracils. The hairpin causes the RNA polymerase to pause and the downstream U-rich sequence destabilizes the RNA-DNA hybrid, promoting dissociation of the transcription complex and release of the RNA transcript.

Terminator efficiency varies with hairpin stability, including stem length, loop size, and GC content, as well as the length of the U-tract. Some terminators function with the aid of the transcription factor NusA, which can influence pausing and termination efficiency in certain bacteria.

Rho-independent termination contrasts with Rho-dependent termination, which relies on the Rho helicase to disrupt elongation at specific sites. Intrinsic terminators are widely distributed in bacterial genomes and are commonly used in operon ends. They can be predicted bioinformatically by searching for inverted repeats followed by poly-U tracts and validated experimentally through in vitro transcription assays.

Overall, intrinsic termination provides a sequence-encoded, Rho-independent means of halting transcription, leveraging RNA structure to regulate gene expression.