Organization and characterization of the ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit ^εN-methyltransferase gene in tobacco

Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) large subunit (LS) ^εN-methyltransferase (Rubisco LSMT) catalyzes the posttranslational methylation of the ε-amino group of Lys-14 in the LS of Rubisco in many higher plant species including tobacco. The tobacco Rubisco LSMT gene (rbcMT-T) and its cDNA were isolated, sequenced, and characterized. The gene contains 6 exons and spans about 6 kb. Primer extension analysis indicated one transcription start site located 93 nt upstream of the translation initiation site. Sequence analysis of the 5′-flanking region suggests several potential binding sites for transcription factors, including 7 GT-1 elements and an HSP-70.5 element. Gene dosage analysis by Southern hybridization demonstrated that the tobacco rbcMT-T gene is present as a single copy in the tobacco haploid genome. The full-length cDNA for tobacco rbcMT-T is 1974 nt in length excluding the 3′ poly(A)₁₅ tail, and encodes a 491 amino acid polypeptide with a molecular mass of ca. 56 kDa. The deduced amino acid sequence of tobacco Rubisco LSMT has 64.5% identity and 75.3% similarity with the sequence of pea Rubisco LSMT, and both proteins contain several copies of a conserved imperfect leucine-rich repeat motif.