Translation limits synthesis of an assembly-initiating coat protein of filamentous phage IKe

Area of Science:

• Molecular Biology
• Virology
• Genetics

Background:

• Filamentous bacteriophages like IKe and Ff (including phages f1, M13, and fd) exhibit distinct DNA sequences but share functional similarities.
• Genes V and VII encode proteins with vastly different expression levels, pV for DNA coating and pVII for phage particle capping.
• Gene V and VII are adjacent on the mRNA, with similar representation in both Ff and IKe phage groups.

Purpose of the Study:

• To investigate the translational control mechanisms governing gene V and VII expression in the IKe filamentous bacteriophage.
• To compare the translational coupling and initiation site activities between IKe and Ff bacteriophage gene VII.
• To understand the reasons behind the severe downregulation of gene VII translation in IKe phage.

Main Methods:

• Comparative analysis of gene V and VII translation in IKe and Ff bacteriophages.
• Assessment of initiation site activity for both genes in each phage group.
• Quantification of translational coupling efficiency between adjacent genes.

Main Results:

• The IKe gene VII initiation site shows detectable activity, unlike the Ff gene VII site, yet coupling is minimal.
• Both IKe gene V and VII initiation sites exhibit higher activity compared to their Ff counterparts.
• A significant translational drop (approximately 75-fold) occurs at the IKe V-VII junction, leading to low gene VII expression.

Conclusions:

• Despite higher intrinsic activity, IKe gene VII translation is severely limited by translational coupling.
• Gene VII expression is maintained at low levels in both IKe and Ff phages, indicating evolutionary selection for this regulation.
• The findings highlight distinct translational control strategies employed by related filamentous bacteriophages.