Mutations in the rho transcription termination factor that affect RNA tracking

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• Rho is a bacterial transcription termination factor essential for regulating gene expression.
• Positively charged amino acids within Rho are hypothesized to play a role in RNA binding and translocation.
• Understanding Rho's structure-function relationship is key to deciphering transcription termination mechanisms.

Purpose of the Study:

• To investigate the role of specific positively charged amino acids in Rho's structure and function.
• To determine the contribution of these residues to ATP hydrolysis and transcription termination.
• To elucidate the organization of the RNA-tracking site in Rho.

Main Methods:

• Site-directed mutagenesis was employed to alter conserved positively charged amino acid residues in Rho.
• In vitro assays were used to measure ATP hydrolysis rates (kcat, Km) and transcription termination efficiencies.
• Kinetic analyses were performed on wild-type and mutant Rho proteins.

Main Results:

• Mutations in positively charged residues N-terminal and C-terminal to the ATP hydrolysis domain significantly reduced Rho's transcription termination efficiency (50-77%).
• Mutated Rho proteins exhibited decreased catalytic rates (kcat) for ATP hydrolysis and increased substrate affinity (Km) for RNA activation.
• Residues surrounding the ATP hydrolysis domain also impacted Rho's kinetic properties.

Conclusions:

• A secondary RNA-tracking site in Rho is formed by positively charged amino acids oriented towards the central hole.
• These residues, clustered above and below the ATP hydrolysis domain, are critical for Rho's function in transcription termination.
• The findings provide insights into the structural basis of Rho-dependent transcription termination.