164-169Covalent 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