The Function of HASTY in Arabidopsis

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The transport of molecules across the nuclear membrane is primarily regulated by members of the importin beta family of proteins. Although the function of these proteins is well characterized in yeast and mammals, very little is known about their function in plants. The experiments described in this project are designed to reveal the function of HASTY, the Arabidopsis orthologue of Exportin5. Exportin5 has been implicated in the nuclear export of miRNAs and tRNAs in mammals, and the mutant phenotype of hasty suggests that it may have a similar function in plants. This hypothesis will be tested by examining the effect of hasty mutations on the sub-cellular distribution of miRNAs and tRNAs, and by identifying the molecules with which the HASTY protein physically interacts in vivo and in vitro. Screens for mutations that suppress the phenotype of hst-3 have been conducted in order to identify genes that are functionally related to HST. Positional cloning will be used to identify the gene affected by one such mutation, soh, and its function will be characterized. At present, HASTY is the only orthologue of Exportin5 in higher organisms for which mutant alleles exist. These mutations provide a unique opportunity to study the function of this important protein, and may provide new insights into the biogenesis and function of miRNAs as well.