Development of functional analysis of genes in cells using functional nucleic acids

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Now that the sequences of many genomes are available, methods are required for the rapid identification of functional genes. We describe here a simple system for the isolation of genes that function in the tumor necrosis factor-α(TNF-α)-mediated pathway of apoptosis, using RNA helicase-associated ribozyme libraries with randomized substrate-binding arms. Because target-site accessibility considerably limits the effective use of intracellular ribozymes, the effectiveness of a conventional ribozyme library has been low. To overcome this obstacle, we attached to ribozymes an RNA motif (poly(A)-tail) able to interact with endogenous RNA helicase(s) so that the resulting helicase-attached, hybrid ribozymes can more easily attack target sites regardless of their secondary or tertiary structures. When the phenotype of cells changes upon introduction of a ribozyme library, genes responsible for these changes may be identified by sequencing the active ribozyme clones. In the case of TNF-α-mediated apoptosis, when a ribozyme library was introduced into MCF-7 cells, surviving clones were completely or partially resistant to TNF-α-induced apoptosis. We identified many pro-apoptotic genes and partial sequences of previously uncharacterized genes using this method. Our gene discovery system should be generally applicable to the identification of functional genes in various systems such as cancer metastasis.