Cloning and Characterization of a Gene Encoding Ubiquitin Conjugating Enzyme from the Mangrove Species, Avicennia marina (Forsk.) Vierh

Covalent attachment of ubiquitin has been implicated in mediating proteolysis of the cellular proteins by ubiquitin-proteasome pathway. Ubiquitin activating enzyme (E1), ubiquitin conjugating enzyme (E2), and ubiquitin protein ligase (E3) are the three enzymes involved in this process. This paper reports the isolation of a gene that codes for the ubiquitin conjugating enzyme in Avicennia marina (AmUBC2), and regulation of its expression at RNA level under salt stress. Deduced amino acid sequence of AmUBC2 showed 96% identity with UBC2 of Arabidopsis thaliana and also 73-78% identity with RAD6 DNA repair protein of Homo sapiens, Rattus norvegicus, Caenorhabditis elegans, Drosophila melanogaster, Arabidopsis thaliana and Saccharomyces cerevisiae. Multiple alignment analysis showed that the amino acid residues in the core region of UBC2 were highly conserved across different taxa in the evolutionary hierarchy. While some ubiquitin conjugating enzymes were induced under salt, heat and heavy metal stress in different tissues in plants, Northern analysis in the present study has clearly shown that the expression of UBC2 is not induced by salt stress either in root or in leaf tissues in A. marina. Southern hybridization of genomic DNA with gene-specific probe showed that AmUBC2 is a single copy gene.