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The use of adenosine N/sup 1/-oxide derivatives to prevent intramolecular cyclization during nucleophilic displacement reactions on the sugar moiety is described. This new synthetic use of N/sup 1/-oxides is illustrated by the synthesis of 5'-O-(p-toluenesulfonyl)-2',3'-O-isopropylideneadenosine N/sup 1/-oxide (6) and subsequent displacement of the 5' substituent with iodide or azide under conditions which lead exclusively to N/sup 3/..-->..5' intramolecular cyclization in the absence of the N/sup 1/-oxide. Similarly, reaction of 2',3'-O-isopropylideneadenosine N/sup 1/-oxide with methyltriphenoxyphosphonium iodide produces 5'-iodo-5'-deoxy-2',3'-O-isopropylideneadenosine N/sup 1/-oxide (7) with no observable cyclization. In addition, 2',3'-anhydroadenosine N/sup 1/-oxide (17) is shown to be stable under conditions that lead to complete N/sup 3/..-->..3' intramolecular cyclization in the upprotected 2',3'-anhydroadenosine (14). Reduction of the N/sup 1/-oxide to produce the parent nucleoside is readily achieved by using hexachlorodisilane or by hydrogenating over Raney nickel. The mechanistical rationale and implications for additional nucleoside transformations are discussed. 2 tables, 1 figure.

The yeast genes RNA2-RNA11 are necessary for splicing of nuclear intron-containing pre-mRNAs. We investigated the relationships among these genes by asking whether increased expression of one RNA gene leads to suppression of the temperature-sensitive lethality of a mutation in any other RNA gene. The presence of extra plasmid-borne copies of the RNA3 gene relieves the lethality of temperature-sensitive rna4 mutations. A region of the yeast genome (SRN2) is described that suppresses temperature-sensitive rna2 mutations when it is present on either medium or high-copy number plasmids. Neither suppression occurs via a bypass of RNA gene function since null alleles of rna2 and rna4 are not suppressed by elevated dosage of SRN2 and RNA3, respectively. These results suggest that the SRN2 and RNA2 gene products have related functions, as do the RNA3 and RNA4 gene products.

A number of environmental stresses can lead to enhanced production of superoxide within plant tissues, and plants are believed to rely on the enzyme superoxide dismutase (SOD) to detoxify this reactive oxygen species. We have identified seven cDNAs and genes for SOD in Arabidopsis. These consist of three CuZnSODs (CSD1,CSD2, and CSD3), three FeSODs (FSD1, FSD2, and FSD3), and one MnSOD (MSD1). The chromosomal location of these seven SOD genes has been established. To study this enzyme family, antibodies were generated against five proteins: CSD1, CSD2, CSD3, FSD1, and MSD1. Using these antisera and nondenaturing-polyacrylamide gel electrophoresis enzyme assays, we identified protein and activity for two CuZnSODs and for FeSOD and MnSOD in Arabidopsis rosette tissue. Additionally, subcellular fractionation studies revealed the presence of CSD2 and FeSOD protein within Arabidopsis chloroplasts. The seven SOD mRNAs and the four proteins identified were differentially regulated in response to various light regimes, ozone fumigation, and ultraviolet-B irradiation. To our knowledge, this is the first report of a large-scale analysis of the regulation of multiple SOD proteins in a plant species.