In an article published online in advance in Science this week, Emily Balskus and Christopher Walsh at Harvard Medical School describe the "genetic and molecular basis for sunscreen biosynthesis in cyanobacteria." They show that a mycosporine-like amino acid biosynthetic gene cluster generates four enzymes in vitro. "In addition to clarifying the origin of the MAAs, these efforts have revealed two unprecedented enzymatic strategies for imine formation," Balskus and Walsh write.