Nucleotide sequence of the Ppc2 gene encoding a housekeeping isoform of phosphoenolpyruvate carboxylase from Mesembryanthemum crystallinum.

The gene encoding a housekeeping form of phospboenolpyruvate carboxylase (EC 4.1.1.31), was isolated from a genomic library of total DNA of Mesembryanthemum crystallinum cloned into Lambda FIX (1) using a cDNA probe specific for the CAM (Crassulacean acid metabolism) form of the enzyme (2). This gene, designated Ppc2, is present as a single copy on the Af crystallinum genome. Unlike Ppcl, the expression of this gene is not induced by salt or drought stress. The coding region of the gene is interrupted by nine introns varying in size from 103 to 1463 nucleotides. Intron placement within the coding region is completely conserved with respect to the CAM-specific form of phosphoenolpynivate carboxlase from M. crystallinum (1) and the C4 pbotosynthetic form of phosphoenolpyruvate carboxlase from maize (3). Ppcl (960 codons) encodes a porypeptide having a predicted molecular weight of 109,041. The PJ?C2 protein shares 83% and 78.2% identity at the amino acid level with the M. cryslalUnum (1) and maize (4) enzymes, respectively. The Ppcl gene product is more distantly related to the phosphcnolpyruvate carboxylase genes from E. coll (5) and A. nldulans (6) having 43 5% and 35.1% amino acid identity, respectively.