A new model for coronavirus transcription

Area of Science:

• Virology
• Molecular Biology
• RNA Synthesis

Background:

• Coronaviruses possess a large positive-sense RNA genome with a 5' cap and 3' polyadenylation.
• Infected cells contain subgenomic mRNAs (sgmRNAs) forming a nested set with the genome, sharing a common 5' leader sequence.
• The mechanism of coronavirus sgmRNA transcription, particularly discontinuous transcription, remains poorly understood and debated.

Purpose of the Study:

• To investigate and propose a new model for coronavirus transcription, termed 3' discontinuous extension of negative strands.
• To challenge the existing leader-primed transcription model by identifying and characterizing key intermediate RNA structures.

Main Methods:

• Identification and separation of replication intermediates (RIs) containing subgenome-length RNA from those with genome-length templates.
• Analysis of the timing of subgenome-length negative strand formation during viral infection.
• Characterization of the 3' end sequences of subgenome-length negative strands, specifically the presence of a leader RNA copy.

Main Results:

• Replication intermediates with subgenome-length templates were found in infected cells and are distinct from genome-length RIs.
• Subgenome-length negative strands form early in infection, coinciding with increased viral RNA synthesis.
• These negative strands contain a complementary copy of the 5' leader RNA at their 3' end, crucial for sgmRNA synthesis.

Conclusions:

• The study provides evidence supporting the 3' discontinuous extension of negative strands model for coronavirus transcription.
• This new model suggests negative strand synthesis is discontinuous, while subgenomic mRNA synthesis is continuous, reversing the leader-primed model's predictions.
• Subgenome-length negative strands arise directly from the genome and acquire their leader sequence via polymerase jumping.