TA1535[pSK1002] tester strain has been used for many years to detect potentially genotoxic test compounds in a 96-well microplate. Upon exposure of the bacterial cells to potentially genotoxic chemicals, biocides, environmental samples, surface, waste or drinking water, the umuC gene is induced as part of the general SOS response. The plasmid pSK1002 contains the umuC gene fused to the lacZ-gene which includes β-galactosidase. Once the umuC-gene is induced it can be assessed by determination of the β-galactosidase activity: conversion of the colorless ONPG substrate (o-nitrophenyl-β-D-galactopyranoside) to the yellow product o-nitrophenyl.

As with other bacterial genotoxicity and mutagenicity assays, compounds requiring metabolic activation for activity can be investigated with the addition of metabolically induced S9 microsomal rat liver fraction.