DARNA uses virus-bound DNA to trigger bacterial growth arrest
Bacteria can distinguish an infection signal through the way a viral protein presents single-stranded DNA. A single peer-reviewed study found that this activates DARNA, a defence system that cuts transfer RNA and arrests the infected cell’s growth. The host bacterium’s DNA-binding protein left the system inactive, a distinction that helps separate infection from a false alarm.
Science··Morning
A viral protein changes how DNA is presented
The bacterial antiviral system DARNA responds to single-stranded DNA when a viral protein makes that DNA accessible. Rugile Puteikiene, Christopher Vassallo and colleagues traced the trigger in a single peer-reviewed study published on October 16. Bacteriophages, the viruses that infect bacteria, carry single-stranded DNA-binding proteins. The viral protein was not itself the direct trigger: the DNA activated DARNA, with its protein context helping distinguish infection from the bacterium’s ordinary activity.[1]
RNA cutting arrests the infected cell
Activated DARNA cut bacterial transfer RNAs in their anticodon loops. These molecules deliver amino acids during protein production; cutting them restricts cell growth and viral propagation. The team combined phages that escaped the defence, genome sequencing, RNA analysis and biochemical tests. Cryo-electron microscopy revealed an assembly containing twelve DARNA subunits. A catalytic-site mutant did not show the same growth arrest, connecting the protein’s cutting activity with the cellular response.[1]
Host proteins did not produce the same alarm
DARNA remained inactive in the presence of the host bacterium’s own DNA-binding protein. Experiments support a distinction based on how viral and host proteins present DNA. Phage escape mutations and changes in DARNA’s catalytic region separately tested activation and RNA cleavage. These controls connect the recognition step to the subsequent growth arrest. The findings concern this bacterial defence system. Growth arrest protects against viral spread at a cost to the infected cell; the work did not test human immunity or treatment in patients.[1]
