Question

Synthesis of RNA molecule is terminated by

• A. $\alpha$-factor
• B. $\gamma$-factor
• C. $\delta$-factor
• D. $\rho$-factor

Answer 1

Answer: (D)

$\rho$-factor

DNA polymerase III is the major polymerizing enzyme with ten types of subunits; polymerization and proof-reading activities reside in its $\alpha$ and $ϵ$ subunits, respectively. The $\theta$, $\alpha$ and $ϵ$ form a core polymerase with polymerization activity but lack processivity which is imparted by clamp-loading complex complex (two copies of $\tau$, $\gamma$, $\delta$ and ${\delta }^{\prime }$ prime subunits. Thus, $\alpha$, $\delta$ and $\gamma$ are subunits of DNA polymerase enzyme which makes option A, B and C are incorrect. The $\rho$ protein binds with the RNA at $\rho$ utilization elements (rut, CA-rich sequence) and moves, in the 5’ to 3’ direction, towards the transcription complex that is paused at a termination site. The ATP-dependent RNA-DNA helicase activity of $\rho$ protein promotes its translocation along the RNA using energy from ATP hydrolysis. The correct answer is D.