Structure-based functional analysis of the replication protein of plasmid R6K: key amino acids at the pi/DNA...

Area of Science:

• Molecular biology
• Genetics
• Biochemistry

Background:

• Plasmid R6K replication relies on the pi protein binding to iteron DNA sequences.
• Previous studies identified critical DNA bases within the iteron for pi protein interaction.

Purpose of the Study:

• To investigate the roles of six specific amino acids (Ser71, Try74, Gly131, Gly211, Arg225, Arg254) in the pi protein.
• To determine the importance of these amino acids for DNA binding and replication initiation.

Main Methods:

• Site-directed mutagenesis of the pir gene encoding the pi protein.
• DNA-binding assays to assess protein-DNA interactions.
• In vivo replication assays to evaluate functional impact.

Main Results:

• Mutations in Ser71, Try74, Arg225, and Arg254 significantly altered pi protein DNA-binding affinity.
• Glycine residues (Gly131, Gly211) appeared less critical for direct DNA contact but may influence protein structure.
• Altered DNA binding correlated with changes in R6K plasmid replication efficiency.

Conclusions:

• Specific amino acids within the pi protein are critical for sequence-specific DNA binding to R6K iterons.
• These findings elucidate the molecular mechanism of pi protein-DNA recognition.
• Understanding these interactions is key for controlling plasmid replication.