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Most readers of this article are not familiar with RNA interference or may even have never heard about this new powerful technology. In a few chapters, this review will guide you step-by-step towards a better understanding of what is RNA interference, how does it work, what should be done, and what should be avoided. With our help, you will discover a new fascinating world: gene suppression through small RNA molecules.

INTRODUCTION

Establishing a convenient and reliable method to knock-out gene expression at the mRNA level has been the dream and nightmare of molecular biologists for the last 15 years. In efforts to generate loss-of function cells or organisms, various molecules that included, for example, antisense sequences, ribozymes, and chimeric oligonucleotides have been tested, but the design of such molecules was based on trial and error, depending on the properties of the target gene. Moreover, the desired effects were difficult to predict, and often only weak suppression achieved (Braasch and Corey, 2002). More than a decade ago, some botanists won the jackpot unconsciously. In 1990, two teams lead respectively by Napoli and Stuitje first reported the cosuppression of an overexpressed chalcone synthase (CHS) in plants. When trying to create more purple petunias, they sometimes achieved an unexpected opposite result (more white petunias!). The mechanism of this curious phenomenon remained a mystery, but it was proposed that the products of degradation of the double-stranded RNA region in the CHS gene might be related to this post-transcriptional gene silencing (PTGS) (Van der Krol et al., 1990 - Jorgensen et al., 1996) (Table 1). In the fungi Neurospora crassa, it was shown that an overexpressed transgene can also induce gene silencing at the post-transcriptional level, a phenomenon referred to as quelling (Romano and Maciano, 1992) (Table 1).……