Analysis of a viral replication repressor: sequence requirements for a large symmetrical internal loop

Area of Science:

• Plant virology
• Molecular biology
• RNA structure-function relationships

Background:

• Carmovirus members possess a conserved 3' hairpin (H5) with a large internal symmetrical loop (LSL).
• This H5 structure acts as a repressor of minus-strand synthesis in satellite RNA (satC).
• H5-mediated repression involves sequestration of the RNA 3' end through base pairing with the LSL.

Purpose of the Study:

• To investigate the role of specific sequences within the satC H5 LSL in RNA accumulation.
• To determine the correlation between RNA replication efficiency and plant accumulation.
• To explore potential functions of the LSL beyond minus-strand synthesis repression.

Main Methods:

• Single site mutational analysis of the satC H5 LSL.
• In vivo genetic selection (SELEX) to identify functional sequences.
• Assessment of satC accumulation in plants and protoplasts.
• Comparison of RNA replication fitness in protoplasts versus whole plants.

Main Results:

• Specific sequences in the middle and upper regions of the LSL are essential for robust satC accumulation.
• Mutations affecting satC accumulation in plants did not always correlate with replication efficiency in protoplasts.
• The LSL's role in regulating satC accumulation appears to extend beyond repressing minus-strand synthesis.

Conclusions:

• The satC H5 LSL contains critical sequence elements necessary for efficient viral RNA accumulation in plants.
• The LSL's function is complex, potentially involving multiple regulatory roles in the viral life cycle.
• Further research is needed to elucidate the full spectrum of LSL functions in Carmovirus replication and pathogenesis.