Route of the sun block: according to empirical evidence, sun-screening mycosporine-like amino acids (MAAs) in Eukarya originate from the shikimic acid pathway, whereas in cyanobacteria, biosynthesis of the MAA shinorine reportedly occurs through the pentose phosphate pathway. However, gene deletion shows that the cyanobacterium Anabaena variabilis ATCC 29143 does not biosynthesise shinorine exclusively by this route.