Molecular characterization of a light-responsive gene, breast basic conserved protein 1 (OsiBBC1), encoding nuclear-localized protein homologous to ribosomal protein L13 from Oryza sativa indica.

Abstract Rice ( Oryza sativa L. subsp. indica ) cDNA for the gene OsiBBC1 , encoding homologue of the breast basic conserved protein 1 (BBC1), similar to ribosomal protein L13, has been identified and characterized. OsiBBC1 codes for a 24 kDa highly basic protein with two potential bipartite nuclear localization signals (NLS) and a transcriptional activation domain (TAD). The structural part of the gene is interrupted by four introns. The OsiBBC1 gene is represented by two copies in the rice genome and both of them are expressed. Northern analysis showed that OsiBBC1 is expressed more in the young root, post-fertilized inflorescence, leaf base and callus tissue, which are comprised of actively dividing cells, indicating its role in cell division. The OsiBBC1 transcript accumulated more in the root of light-grown seedlings as compared to the shoot while its levels were higher in the shoot as compared to root of the etiolated seedlings, indicating its down-regulation by light. The western analysis, carried out using antibodies raised against a recombinant fusion protein, 6xHis–OsiBBC1, corroborated its tissue-specific expression profile observed by northern analysis. In addition, OsiBBC1/RPL13 protein could be targetted to the nucleus by particle bombardment of OsiBBC1::GUS fusion construct in the onion epidermal cells.