A hybrid molecule generated by fusing the regulatory domain of PKC-delta with the catalytic domain of PKC-zeta is, like PKC-delta but unlike PKC-zeta, a phorbol ester-dependent enzyme. However, the substrate specificity of this hybrid resembles that of PKC-zeta. Expression of mammalian PKC-delta, but not PKC-zeta, in the fission yeast Schizosaccharomyces pombe causes growth retardation and phorbol esters amplify the PKC-delta phenotype without affecting that of PKC-zeta (Goode et al., submitted). The chimaeric molecule also inhibited growth and this effect was phorbol-ester dependent. Both the hybrid and PKC-delta holoenzyme, in contrast to PKC-zeta, down-regulate upon prolonged exposure to phorbol esters in vivo. Thus, this hybrid retains the regulatory properties conferred by PKC-delta but the catalytic properties of PKC-zeta. This regulatable chimaeric molecule will be useful in assessing the function of PKC-zeta.