Gene sll0033 from Synechocystis 6803 encodes a carotene isomerase involved in the biosynthesis of all-E lycopene.

The function of gene sll0033 from Synechocystis 6803 which is homologous to the bacterial crtI-type phytoene desaturase genes was elucidated as a novel carotene isomerase. Escherichia coli transformed with all genes necessary for the formation of zeta-carotene and expressing a zeta-carotene desaturase synthesized the positional isomer prolycopene (7,9,7',9'Z lycopene) which cannot be cyclized in the subsequent reactions to a- and beta-carotene. Upon cotransformation with sll0033, the formation of all-E lycopene is mediated instead.