A Tubulin promoter drives expression of the C-terminal part of cic (contains the C2 and C1 domains, but lacks the DNA-binding domain), tagged at the N-terminal end with a nuclear localization signal, and at the C-terminal end (via a GGGSGGGS linker) with mScarlet. This transgene can be used as a sensor for measurement of endogenous levels of rl (ERK) activity.