CLONING AND EXPRESSION OF THE SOYBEAN CHLH GENE ENCODING A SUBUNIT OFMG-CHELATASE AND LOCALIZATION OF THE MG2-DEPENDENT CHLH PROTEIN WITHIN THE CHLOROPLAST( CONCENTRATION)

From the soybean cDNA library, we isolated and analyzed the chlH gene encoding a subunit of Mg-chelatase. The subunit was a polypeptide of 1 ,383 amino acids with a molecular mass of 153,491 Da, which shared 90% identity with the olive gene from Antirrhinum majus. The regulation o f the expression of chlH was investigated in photomixotrophic soybean suspension cells (SB-P), The expression was light-inducible, and the i nduction was more rapid than those of chlI and cab2. Furthermore, the levels of the transcripts and products of chlH appeared to be regulate d by a circadian oscillation, The subchloroplastic localization of Chl H was investigated by immunoblot analyses with antiserum against recom binant ChlH, Depending on the concentration of Mg2+ in the lysis buffe r, the localization of ChlH protein migrated between the stroma and th e envelope membrane; ChlH was localized on the envelope membrane, a ma jor site of chlorophyll biosynthesis, when the Mg2+ concentration of t he lysis buffer was high (above 5 mM), These results indicated that th e activity of Mg-chelatase was regulated by modulation of the expressi on and subchloroplastic localization of ChlH protein.