Calcineurin, a protein phosphatase required for Ca 2؉ signaling in many cell types, is a heterodimer composed of catalytic and regulatory subunits. The fission yeast genome encodes a single set of catalytic (Ppb1) and regulatory (Cnb1) subunits, providing an ideal model system to study the functions of these subunits in vivo. Here, we cloned the cnb1 ؉ gene and showed that the cnb1 knock-out (⌬cnb1) exhibits identical phenotypes with ⌬ppb1 and that overexpression of Ppb1 failed to suppress the phenotypes of ⌬cnb1. Interestingly, overexpression of the C-terminal-deleted Ppb1 (Ppb1⌬C), the constitutively active form of Ppb1, also failed to suppress the phenotypes of ⌬cnb1. FK506 caused MgCl 2 sensitivity to the wild-type cells in an FKBP12-dependent manner. Co-overexpression of Ppb1 and Cnb1 suppressed the FK506-induced MgCl 2 sensitivity, but the suppression was only partial, suggesting that an excess amount of the Ppb1-Cnb1 complex cannot compete out the FKBP12-FK506 complex. Although overexpression of Ppb1⌬C alone had little effect on cell growth, cooverexpression of Ppb1⌬C and Cnb1 caused a distinct growth defect. FK506 suppressed the growth defect when Cnb1 was co-expressed using the attenuated nmt1 promoter, but it failed to suppress the defect when Cnb1 was co-expressed using the wild-type nmt1 promoter. Knock-out of the prz1 ؉ gene, encoding a downstream target transcription factor of calcineurin, suppressed the growth defect irrespective of the promoter potency. These results suggest that Cnb1 is essential for the activation of calcineurin and that the activated calcineurin is the pharmacological target of the FKBP12-FK506 complex in vivo.

Carbon-carbon bond formations at the benzylic positions of N-benzylxanthone imines and N-benzyldi-1-naphthyl ketone imine

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