Expression of a gene for cyclophilin which contains an amino-terminal endoplasmic reticulum-targeting signal

We isolated a novel gene for cyclophilin (CyP) first identified as an intra cellular target of the immunosuppressant cyclosporin A and also known to ha ve peptidyl-prolyl cis-trans isomerase (PPIase) activity, named A TCYP5 fro m Arabidopsis thaliana. A TCYP5 encoded a polypeptide with 201 amino acids with a putative ER-targeting signal sequence at its N-terminal, but without the typical ER-retention signal in its C-terminal. In addition, ATCYP5 pro tein contained a seven amino-acid long sequence which has been found previo usly only in cytosolic CyPs from plants. The synthetic mutant green fluores cent protein (sGFP; S65T) was fused to the N-terminal part of ATCYP5, and e xpressed in tobacco BY-2 cells. The fluorescence derived from the fusion pr otein was detected mainly around the nucleus, indicating translocation into ER. ATCYP5 was expressed mainly in young stems especially in the apical re gion and weakly in leaves and roots.