It’s not just us that get attacked by viruses, bacteria are vulnerable too. They’re locked in a war of evolution with their viral attackers, one which we can benefit from. This is a 3D model of CRISPR, a bacterial defence system made up of protein bits (coloured ribbons) wrapped around a loop of RNA (green), a bit like fingers around a knuckle duster (but 10 million times smaller). This ‘surveillance complex’ detects specific sequences of viral DNA, calling in reinforcements to destroy what it finds. But the virus has evolved countermeasures. Anti-CRISPR proteins (red and light green clumps) block the surveillance complex, preventing it scanning. Most cunningly of all, the virus targets crucial parts of CRISPR that can’t adapt without disabling the defences completely. In the future, researchers exploiting CRISPR’s detection powers for gene therapy in human diseases may take advantage of anti-CRISPR proteins as a quick on/off switch.
Written by John Ankers
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