Isolation and characterisation 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 library with homologous cDNA fragments from Arabidopsis thaliana. A full-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 amplification of cDNA ends' (RACE) method. Both genes Chl I and Chl H were strongly expressed in young leaves and to a lesser extent in mature leaves. Only traces of both transcripts were found in flowering organs. Southern blot analysis suggests that CHL I is encoded by a single gene and CHL H most likely by several genes.