To downregulate expression of the β1 integrin subunit in endothelial cells, plasmid encoding the ribozyme cassette containing hammerhead ribozyme flanked at the 5' terminus by tRNAVal and at the 3' terminus by constitutive transport element sequences was constructed. When used to transfect immortalized human endothelial cell line EA.hy 926, it selectively blocked the synthesis of the β1 integrin subunit and thus inhibited migration and proliferation of the cells. Thus, this construct may be a valuable tool to control the proangiogenic phenotype of stimulated endothelial cells.
Viroids are small (about 300 nucleotides), single-stranded, circular, non-en- capsidated pathogenic RNA molecules. They do not code for proteins and thus depend on plant host enzymes for their replication and other functions. They induce plant diseases by direct interaction with host factors but the mechanism of pathogenicity is still unknown. They can alter the expression of selected plant genes important for growth and development. Viroids belong to two families, the Avsunviroidae and the Pospiviroidae. Viroids of the Avsunviroidae family adopt a branched or quasi rod-like secondary structure in their native state. Members of the Pospiviroidae family adopt a rod-like secondary structure. In such native structures five structural/functional domains have been identified: central (C), pathogenicity, variable and two terminal domains. The central conserved region (CCR) within the C domain characterizes viroids of the Pospiviroidae. Specific secondary structures of this region play an important role in viroid replication and processing. Viroids of the Avsunviroidae family lack a CCR but possess self-cleaving properties by forming hammerhead ribozyme structures; they accumulate and replicate in chloroplasts, whereas members of the Pospiviroidae family have a nuclear localization. Viroid replication occurs via a rolling circle mechanism using either a symmetric or asymmetric pathway in three steps, RNA transcription, processing and ligation.
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