5xlexAop regulatory sequences drive expression of a constitutively active form of Rac1 (amino acid residue 12 has been mutated to Val). Target sequences of 'rCD2 miRNA 6' (a miRNA that targets Rattus norvegicus Cd2 gene) have been inserted into the 5'UTR sequence, rendering this transcript susceptible to silencing by rCD2 miRNA 6.