The radical SAM enzyme spore photoproduct lyase employs a tyrosyl radical for DNA repair.

The spore photoproduct lyase is a radical SAM enzyme, which repairs 5-(α-thyminyl)-5,6-dihydrothymidine. Here we show that the enzyme establishes a complex radical transfer cascade and creates a cysteine and a tyrosyl radical dyade to establish repair. This allows the enzyme to solve topological and energetic problems associated with the radical based repair reaction.