Opening the closed ribosome-binding site of the lysis cistron of bacteriophage MS2

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• Gene expression regulation in prokaryotes primarily occurs at transcriptional and translational levels.
• Translational control, particularly at initiation, is crucial for protein synthesis regulation.
• Polycistronic messenger RNAs (mRNAs) often utilize translational coupling for sequential gene expression, preventing premature translation of downstream genes.

Purpose of the Study:

• To investigate the structural features in MS2 bacteriophage RNA that prevent ribosome access to the lysis (L) cistron's start codon.
• To understand the mechanism of translational coupling for the L cistron in MS2 RNA.
• To identify specific RNA structural elements responsible for inhibiting L cistron translation initiation.

Main Methods:

• Analysis of MS2 RNA secondary structure.
• Introduction of small deletions in the MS2 RNA sequence, approximately 40 nucleotides upstream of the L gene start codon.
• Assessment of L cistron translation following RNA modifications.

Main Results:

• Specific RNA structural features were identified as barriers to ribosome binding at the L cistron initiation site.
• Small deletions near the L gene start codon successfully removed the initiation barrier.
• The modified MS2 RNA allowed for independent translation of the L cistron, bypassing the need for ribosome passage over the coat cistron.

Conclusions:

• The initiation of lysis (L) cistron translation in MS2 bacteriophage is actively repressed by RNA structure.
• Modifying the RNA structure by introducing deletions can alleviate this repression, enabling independent L cistron translation.
• A proposed RNA secondary structure explains the mechanism by which the ribosome binding site is kept inaccessible.