To cope with DNA alkylation damage, cells have evolved genes that encode proteins with alkylation-specific DNA repair activities. It is notable that these repair systems are conserved from bacteria to humans . In Escherichia coli, cells exposed to a low concentration learn more of an alkylating agent, such as N-methyl-N’-nitro-N-nitrosoguanidine (MNNG) or methyl methanesulfonate (MMS), show a remarkable increase in resistance to both the lethal and mutagenic effects of subsequent high-level challenge treatments with the
same or other alkylating agents [7, 8]. This increased resistance has been known as “”adaptive response”" to alkylation damage in DNA. To date, four Selleck BIIB057 genes have been identified as components of this response, ada, alkA, alkB and aidB. The ada gene encodes
the Ada protein, which has the dual function of a transcriptional regulator for the genes involved in the adaptive response, and a methyltransferase that demethylates two methylated bases (O6meG and O4meT) and methylphosphotriesters produced by methylating agents in the sugar phosphate backbone [6, 9]. When methylated at Cys-69, Ada is converted to a potent activator for the transcription of the ada and alkA, alkB and aidB genes by binding to a consensus sequence referred to as an “”Ada box”" present in the promoter. The alkA gene encodes a glycosylase that repairs several different methylated bases, and the alkB gene, which forms a small operon with the ada gene, is required for error-free replication of methylated single-stranded DNA . The aidB gene encodes the protein that appears to detoxify nitrosoguanines and to reduce the level of methylation by alkylating agents. Early studies
have shown that the expression of the ada-alkB operon, alkA and aidB genes is KU 57788 positively controlled by Ada protein, after it interacts with methylated DNA [11–14]. In contrast, Ada protein also plays a pivotal role in the negative modulation of its own synthesis, and consequently, in the down-regulation of the adaptive response. The carboxyl-terminus of Ada protein appears to be necessary for this negative regulatory function; thus, Ada protein can act as both a positive Vorinostat chemical structure and a negative regulator for the adaptive response of E. coli to alkylating agents . The transcriptional activity of E. coli Ada protein is also directly regulated by posttranslational covalent modification; however, the regulatory components and pathways controlling the adaptive response have not been well studied. Recent advances in functional genomics studies have facilitated understanding of global metabolic and regulatory alterations caused by genotypic and/or environmental changes. DNA microarray has proven to be a successful tool for monitoring genome-wide expression profiles at the mRNA level.