ISOLATION AND CHARACTERIZATION OF TOBACCO (NICOTIANA-TABACUM) CDNA CLONES ENCODING PROTEINS INVOLVED IN MAGNESIUM CHELATION INTO PROTOPORPHYRIN-IX

We have identified cDNA clones encoding the two Mg chelatase subunits CHL I and CHL H from tobacco (Nicotiana tabacum) by screening a cDNA l ibrary with homologous cDNA fragments from Arabidopsis thaliana. A ful l-length Chl I cDNA clone encodes a peptide with 426 amino acids. The entire cDNA sequence encoding 1382 amino acid long CHL H was obtained by extension of a truncated cDNA fragment using the 'rapid amplificati on of cDNA ends' (RACE) method. Both genes Chl I and Chl H were strong ly expressed in young leaves and to a lesser extent in mature leaves. Only traces of both transcripts were found in flowering organs. Southe rn blot analysis suggests that CHL I is encoded by a single gene and C HL H most likely by several genes.