Molecular cloning and sequencing of a cDNA encoding the maize ( Zea mays L.) acyl carrier protein (ACP); comparison to other ACP genes and ACPs

Abstract

A maize cDNA clone containing the acyl carrier protein (ACP) gene has been purified from a commercial library. It codes for a polypeptide of 121 amino acids. The transit peptide exhibits a very high similarity (72%) to the partial sequence of the transit peptide of the ACP-III of barley, another monocotyledon. The amino acid sequence of the mature maize ACP exhibits a high similarity to all monocotyledonous (85%) and dicotyledonous ACP (79%). The maize ACP transit peptide and mature ACP have the following characteristics in common with the corresponding polypeptides in the other plants studied so far. The plant ACP transit peptides contain about 87% uncharged and non-polar residues, 13% positively charged residues and almost no negatively charged residues. They are particularly rich in serine, a feature found in other transit peptides. The transit peptides of the various plant families studied so far do not show any common sequence, which suggests that the three-dimensional structure may be important for the import of the precursor into the chloroplast. On the contrary, most of the plant ACP transit peptide sequences show a SC↓AAK cleavage site motif. The mature plant ACPs contain only 65% uncharged and non-polar residues, and 56% hydrophobic or weakly hydrophobic residues. They contain 12% positively charged residues and 23% negatively charged residues. They have a very highly conserved domain responsible for the binding of 4′-phosphopantetheine to ACP. The sequence shows an α-helix structure just ahead of a hydrophobic sequence whose residues are supposed to be turned towards the interior of the ACP molecule.