CLONING, CHARACTERIZATION AND TRANSIENT EXPRESSION OF THE GENE ENCODING A RICE U3 SMALL NUCLEAR-RNA

A rice U3 small nuclear RNA (snRNA)-encoding gene has been isolated. T he coding region of this gene contains all five conserved sequence box es common to plant U3 snRNAs. The upstream and downstream regions of t he gene harbour characteristic sequence elements required for transcri ption with RNA polymerase III (pol III), as well as three monocot-spec ific promoter (MSP) elements [Connelly et al., Mol. Cell Biol. 14 (199 4) 5910-5919], two of them comprising a palindromic G+C-rich segment. The sequence (TTTAAAA) of the TATA-box in this gene does not fit the e stablished consensus [Marshallsay et al., Plant Mol. Biol. 19 (1992) 9 73-983], making this gene unique among reported snRNA-encoding genes o f plants. An RNase protection assay showed that the gene is expressed properly in cucumber protoplasts. We thus suggest that, with other pro moter elements present, the TATA-box for RNA pol III-specific snRNA-en coding genes may not be as well conserved as that for RNA pol II-speci fic genes.