Primary structure of the soybean nodulin-35 gene encoding uricase II localized in the peroxisomes of uninfected cells of nodules.

Nodulin-35 (N-35), a subunit of nodule-specific uricase (uricase II) of soybean (Glycine max), is shown to be preferentially synthesized on free polysomes during nodule development and is localized in peroxisomes of the uninfected cells of this tissue. A cDNA clone, isolated by using mRNA from immunoprecipitated polysomes, revealed the primary structure of this protein with a molecular mass of 35,100. That this clone represents N-35 was confirmed by comparing the deduced amino acid sequence with the partial sequence of a CNBr-cleaved peptide of purified N-35. Southern blot hybridizations with genomic DNA suggest that there are several EcoRI fragments containing N-35 sequences. Three of these sequences were isolated from a genomic library of soybean. Nucleotide sequence analysis showed that the complete gene extends almost 5000 base pairs on two EcoRI fragments and the coding region (309 codons) is interrupted by seven introns ranging in size from 154 to 1341 base pairs. Lack of a signal sequence and its translation on free polysomes suggest that N-35 is posttranslationally transported to the peroxisomes. Furthermore, there is no cross-hybridization of N-35 cDNA with RNA from young (3- to 4-day) roots and leaves, indicating that the observed "uricase" activity in these tissues is due to the product of a different gene.