ABSTRACT
Regulation of gene expression is an intricate process involving acetylation and deacetylation of histones, methylation and demethylation of cytosine and trans-and cis-acting elements in addition to several transcription factors. Microarray analysis of cellular mRNAs indicate several genes both up-and down-regulated in various pathological conditions of diseases. Over and under expressions of one or one set of genes often effects the expression of other set of genes. Molecules that can specifi cally silence expression of a gene are powerful research tools and perhaps, prospective therapeutics [Anderson 1998]. Much effort has been put into the development of such molecules and has resulted in the creation of different classes of potential therapeutic agents. Singlestranded nucleic acids have the ability to alter gene-expression by binding to and consequently interfering with the stability or function of a target mRNA transcript. The major classes of antisense agents currently used by investigators for sequence-specifi c mRNA knockdown are RNA interference ( RNAi) associated with small interference RNA ( siRNA) and microRNA ( miRNA), ribozymes, DNAzymes, oligonucleotide decoys and antisense oligonucleotides (ODNs), (Figure 1). Selective gene silencing by nucleic acid enzymes has provided researchers with a new strategy to block gene expression to either understand the function of target genes or drug target validation as potential therapeutics.
