Analysis of E. coli rho factor: mutations affecting secondary-site interactions

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• The rho protein is crucial for transcription termination in bacteria.
• It interacts with RNA at distinct primary and secondary binding sites.
• Understanding these interactions is key to elucidating termination mechanisms.

Purpose of the Study:

• To define and differentiate the roles of primary and secondary RNA binding sites in rho protein function.
• To investigate how specific mutations affect rho protein's RNA interaction and activity.

Main Methods:

• Analysis of rho protein mutant alleles (rho-115 and rhosuA1).
• Site-directed mutagenesis to create single-residue changes (KE352, GV99, PH235).
• Biochemical assays measuring RNA binding affinity (Km), helicase, ATPase, and in vitro transcription termination activities.

Main Results:

• Mutations KE352 and GV99 impaired secondary-site RNA activation, showing significantly higher Km values for r(C)10 compared to wild-type.
• These defects correlated with reduced helicase and ATPase activities and loss of in vitro transcription termination.
• The PH235 mutation demonstrated enhanced secondary-site RNA interaction (low Km) and hyperactive ATPase, helicase, and termination capabilities.

Conclusions:

• Mutations at distinct locations in the rho protein can modulate secondary-site RNA activation.
• Secondary-site RNA interactions are pivotal for rho protein's ATP hydrolysis, helicase activity, and transcription termination.
• This study differentiates the functional roles of primary and secondary RNA binding sites in rho-mediated transcription termination.