An Atriplex nummularia cDNA with Sequence Relatedness to the Algal Caltractin Gene

Calcium controls numerous cellular processes with a high degree of spatial and temporal precision. One way by which these controls are effected is through the transduction of a Ca2" signal by an interaction of the cation with Ca2"-binding proteins. Among the Ca2"-binding proteins that are presumed to function in the modulation of cellular processes are calmodulin, troponin C, myosin light chain, parvalbumin, and caltractin (2, 3, 7, 8, 10). Caltractin is a 20-kD Ca2"-binding protein that was isolated from basal body complexes of the unicellular green alga Chlamydomonas reinhardtii (6). The primary structure of caltractin, deduced from peptide fragments and cDNA sequences (5, 6), has 45 to 48% identity with calmodulins and 50% identity with Saccharomyces cerevisiae CDC31-encoded protein (1) that is required for spindle pole body formation. We describe here an Atriplex nummularia cDNA sequence that encodes a predicted peptide with high sequence identity to caltractin (Table I). The 970-base pair cDNA contains a longest open reading frame of 501 nucleotides, with a translated peptide of 167 amino acids that has a molecular mass of 20.3 kD (Fig. 1). The predicted protein is hydrophilic and has a theoretical isoelectric point of 4.7. It is of similar size (167 versus 169 amino acids) to caltractin and has an analogous predicted isoelectric point (4.7 versus 5.3). The sequence identities/similarities between the A. nummularia peptide and caltractin, yeast CDC31 gene product, animal calmodulins, plant calmodulins, and troponin C are 62/82, 42/64, 48/66, 46/65, and 38/68%, respectively. The A. nummularia cDNA contains a CTGCAC sequence that is tandemly repeated seven times just downstream from the putative TGA stop codon (Fig. 1). No discernable consen-