Nucleotide Sequence of a cDNA from Carthamus tinctorius Encoding a Glycerol-3-Phosphate Acyl Transferase

Abstract

GPAT (EC 2.3.1.15) catalyzes the first step in phospholipid and triglyceride synthesis. In the former context, it is implicated in chilling resistance in plants, through its role in selecting the fatty acids that are incorporated into chloroplast lipids and then into membranes. The GPAT from chillingresistant plants such as pea is highly selective for oleic acid, whereas the enzyme from chilling-sensitive plants can incorporate either palmitic or oleic acid at the sn-1 position. The basis of this enzyme specificity is unknown. It is hoped that comparison of GPAT protein sequences from diverse sources may shed some light onto the structural features relevant to enzyme specificity as well as other structural and functional attributes. GPAT exists in both plastidic and extraplastidic forms. The plastidic form has been purified to various degrees from cocoa bean seeds (Fritz et al., 1986), pea leaves (Frentzen et al., 1983; Douady and Dubacq, 1987; Weber et al., 1991), and spinach leaves (Frentzen et al., 1983). The cDNA sequences of chloroplast GPATs from Arabidopsis thaliana (Nishida et al., 1993), cucumber (GenBank accession number M80571), pea (Weber et al., 1991), and squash (Ishizaki et al., 1988) have been reported. Here we present the nucleotide sequence of a full-length cDNA encoding a GPAT isolated from a Xgt22 cDNA library made from mRNA from developing Carthamus tinctorius seeds (Table I). The deduced amino acid sequence exhibits 56.4, 58.5, 57.9, and 53.6%