Question

Compare and contrast Rho-dependent and Rho- independent termination. What features do they have in common and in what ways do they differ?

Answer 1

Both the Rho-dependent and Rho-independent are types of termination mechanism seen in bacteria and prokaryotes. The major difference seen in both types of termination mechanism is presence of a Rho protein in the Rho-dependent type of termination exclusively. The Rho protein is a transcription termination factor which helps in the process of transcription termination.

Rho-Independent Termination

It is also called as intrinsic termination which is a termination mechanism observed in RNA transcription process. In this process, there is no Rho transcription factor that participates in the process. The mRNA contains sequence which has the ability to base pair with itself and forms stem loop like structure. It has a series of U-residues in the transcribed RNA that is preceded by GC rich self complementary region with several intervening nucleotides. Such self complementary region self base pairs with itself and form stem-loop like structure. The stem loop like structure interacts with RNA polymerase causing it to pause. This is how the termination takes place in Rho-independent process.

Rho-Dependent Termination

This type of termination depends on Rho protein and it binds to the un-translated naked RNAs and terminates the synthesis of mRNA. Rho is a RNA/DNA helicase which dissociates RNA polymerase from DNA template to release RNA and it derives its energy through ATP hydrolysing in an RNA-dependent ATPase activity which brings about the process of termination. The Rho protein is initiated by sequences that are rich in cytosine but poor in guanine. It binds to newly formed RNA chain and moves along the molecule in 5’-3’ direction as the RNA polymerase continues to form the mRNA strand. Rho uses ATP hydrolysis to move up the mRNA and meets the RNA polymerase. The RNA polymerase pauses as soon Rho meets the RNA polymerase. The Rho unwinds the RNA-DNA hybrid in the transcription bubble which terminates the transcription and RNA is released.