Cloning, characterization and mRNA expression analysis of PVAS1, a type I asparagine synthetase gene from Phaseolus vulgaris

A gene encoding a putative asparagine synthetase (AS; EC 6.3.5.4) has been isolated from common bean (Phaseolus vulgaris L.). A 2-kb cDNA clone of thi s gene (PVAS1) encodes a protein of 579 amino acids with a predicted molecu lar mass of 65.265 Da, an isoelectric point of 6.3, and a net charge of -9. 3 at pH 7.0. The PVAS1 protein sequence conserves all the amino acid residu es that are essential for glutamine-dependent AS, and PVAS1 complemented an Escherichia coli asparagine auxotroph, which demonstrates that it encodes a glutamine-dependent AS. The PVAS1 protein showed the highest similarity t o soybean SAS1, and piled up with other legume ASs to form an independent d endritic group of type-I AS enzymes. Northern blot analyses revealed that t he expression pattern of PVAS1 resembles that of PVAS2, another AS previous ly described in the common bean. Unlike PVAS2. however, PVAS1 was not expre ssed in the nodule and was not repressed by light, suggesting different fun ctions for these two AS genes.