A modifiedEscherichia coli chaperonin (groEL) polypeptide synthesized in tobacco and targeted to the chloroplasts

The coding region for theEscherichia coli groEL (chaperonin-60) polypeptide was fused downstream of a pea rubisco small subunit transit peptide coding sequence under the control of a tandem 35S CaMV promoter. Transgenic tobacco plants (Nicotiana tabacum cv. Xanthi) containing this modifiedgroEL gene were produced. The modified groEL polypeptide was correctly imported into chloroplasts and accumulated to high or low levels in different plants. The majority of the modified groEL polypeptide was processed correctly to the mature form within the chloroplasts. Approximately 20% of the imported polypeptides retained a portion of the N-terminal transit peptide (TPgroEL). Both groEL and TPgroEL polypeptides assembled into tetradecameric species in the chloroplasts. In plants accumulating high levels of these products, the majority of the plant chaperonin-60 polypeptides in the chloroplast were present in novel hybrid tetradecameric species containing both bacterial and plant chaperonin-60 polypeptides. In plants accumulating low levels of groEL, the predominant species present appeared to be authentic plant cpn60₁₄ and authentic bacterial groEL₁₄. The growth and development of transgenic and control tobacco plants were indistinguishable.Abbreviations cpn60 chaperonin-60 - cpn10 chaperonin-10 - hsp heat shock protein - rubisco ribulose-1,5-bisphosphate carboxylase-oxygenase - ssu small subunit - spp stromal processing peptidase - SDS sodium dodecyl sulfate - PAGE polyacrylamide gel electrophoresis