Structural basis for RNA-genome recognition during bacteriophage Qβ replication

Area of Science:

• Molecular Biology
• Virology
• Structural Biology

Background:

• Bacteriophage Qβ infection involves the formation of a replicase complex for viral genome amplification.
• The Qβ replicase holoenzyme comprises viral and host factors, including translation elongation factors and ribosomal protein S1.
• Understanding the precise roles of viral subunits and host factors in RNA recognition is crucial.

Purpose of the Study:

• To elucidate the roles of the bacteriophage Qβ replicase β-subunit and ribosomal protein S1 (specifically OB1-2 domains) in recognizing the Qβ (+)-RNA genome.
• To investigate the structural basis for Qβ RNA recognition by the replicase complex.
• To understand template discrimination during viral RNA replication initiation.

Main Methods:

• X-ray crystallography
• NMR spectroscopy
• Sequence conservation analysis
• Surface electrostatic potential mapping
• Site-directed mutagenesis

Main Results:

• Identified a basic residue patch on the β-subunit adjacent to the OB2 domain of protein S1.
• NMR spectroscopy confirmed RNA interaction with the OB2 domain.
• Mutagenesis of these basic residues abolished phage infectivity and in vitro RNA amplification, but not replication of smaller RNAs.
• Demonstrated cooperative binding of the β-subunit and protein S1 to the Qβ genome.

Conclusions:

• The β-subunit and protein S1 cooperatively bind the Qβ (+)-RNA genome during replication initiation.
• Specific basic residues on the β-subunit and the OB2 domain of S1 are critical for Qβ genomic RNA recognition.
• These findings provide insights into template discrimination mechanisms in viral RNA replication.