Characterization and gene expression of nodulin Npv30 from common bean

We previously reported that transcripts for a 30-kD nodulin (Npv30) are very abundant in the nodule. In this paper we describe the isolation and characterization of Npv30 cDNA and genomic clones. Npv30 has the following characteristic features: (a) a putative signal sequence at the deduced amino-terminal region, (b) a proline-rich stretch at the carboxy terminus, and (c) a characteristic domain of four cysteines that resemble metal-binding sites. In Phaseolus vulgaris L., Npv30 is encoded by a small gene family that shares discrete sequence homologies with another small gene family in soybean. An antibody against a beta-galactosidase-Npv30 fusion protein detected two proteins of 28 and 30 kD. Although Npv30 transcripts are very abundant, they encode proteins that are hardly detected in nodule fractions, suggesting that these proteins have a short half-life and/or the mRNAs are strongly regulated at the translational level. Npv30 transcripts were detected in the infected cells of the nodule by in situ hybridization experiments.