Primary structure of the soybean nodulin-23 gene and potential regulatory elements in the 5′-flanking regions of nodulin and leghemoglobin genes

Abstract

The nodulin-23 gene of soybean is one of the most abundantly transcribed genes induced during symbiosis with Rhizobium. Using a plasmid (pNod25) from a nodule cDNA library, we have isolated the nodulin gene from a soybean genomic library. Nucleotide sequence analysis of the cDNA and of the genomic clone indicated that the coding region of this gene is 669 bp long and is interrupted by a single intron of about 53ø bp. The deduced protein sequence suggests that nodulin-23 may have a signal sequence. The 5′-flanking sequence of two other nodulin genes, nodulin-24 encoding for a mambrane polypeptide and one of the leghanoglobin genes (LbC₃), were obtained. Comparison of these sequences revealed three conserved eg ions, one of which, an octanucleotide (GTTTCCCT), has 1øø% homology. The conserved sequences are arranged in a unique fashion and have a spatial organization with respect to order and position, which nay suggest a potential regulatory role in controlling the expression of nodulin and leghanoglobin genes during symbiosis.