Structure of the giant RNA polymerase ejected from coliphage N4.

Area of Science:

• Structural Biology
• Virology
• Molecular Biology

Background:

• Schitoviruses are prokaryotic viruses that package a large virion-associated RNA polymerase (vRNAP).
• During infection of Gram-negative bacteria, vRNAP and ejection proteins form a DNA-ejectosome for viral replication.
• The structural and mechanistic details of vRNAP delivery and function remain largely uncharacterized.

Purpose of the Study:

• To elucidate the structure of the coliphage N4 virion-associated RNA polymerase (vRNAP).
• To characterize the roles of phage proteins in vRNAP ejection into host bacteria.
• To understand the mechanism of protein translocation through biological channels during viral infection.

Main Methods:

• Integrative structural analysis of coliphage N4 vRNAP (gp50).
• Comparative analysis of intact and genome-released virions.
• Structural and functional characterization of phage ejection proteins (gp51, gp52) and tail components.

Main Results:

• Coliphage N4 vRNAP is a multi-domain, single-chain enzyme structurally distinct from other known RNAPs.
• vRNAP possesses an intramolecular allosteric regulation mechanism mediated by its C-terminal domain.
• Phage proteins gp51 and gp52 form complexes that create pores for vRNAP release, orchestrated by a tail signaling hub.

Conclusions:

• The unique 'beads-on-a-string' architecture of N4 vRNAP facilitates translocation through narrow biological channels.
• N4 provides a novel model for studying the translocation of large protein complexes across cellular membranes.
• Understanding this mechanism offers insights into viral infection strategies and protein transport.