HSV-1 origin binding protein UL9 forms intermolecular DNA tethers and intramolecular DNA loops

Area of Science:

• Virology
• Molecular Biology
• Genetics

Background:

• Herpesviruses, including HSV-1, are common human pathogens with complex dsDNA genomes.
• Replication initiation of the HSV-1 genome is crucial but not fully understood at the molecular level.
• The origin-binding protein UL9 was hypothesized to loop the oriS sequence to facilitate replication.

Purpose of the Study:

• To directly test the hypothesis that HSV-1 UL9 protein loops the oriS replication origin.
• To investigate the DNA binding and looping capabilities of the UL9 protein.

Main Methods:

• Single-molecule approaches were employed to analyze UL9-DNA interactions.
• Experiments focused on observing UL9's ability to interact with and loop the oriS sequence.
• UL9's DNA looping and tethering activities were assessed at both origin and non-origin sequences.

Main Results:

• Contrary to the prevailing hypothesis, UL9 did not efficiently loop the oriS sequence.
• UL9 demonstrated a high efficiency in forming large DNA loops at non-origin DNA sequences.
• UL9 was shown to effectively tether two separate oriS DNA molecules intermolecularly.

Conclusions:

• The findings challenge the long-standing model of UL9-mediated oriS looping for replication initiation.
• UL9's demonstrated ability to form loops at non-origin sites and tether DNA molecules suggests alternative roles.
• UL9 may play a role in replication initiation through mechanisms other than direct oriS looping, potentially involving DNA tethering for recombination.