• Usha Vijayraghavan

      Articles written in Journal of Genetics

    • Prp21, a U2-snRNP-associated protein, and Prp24, a U6-snRNP-associated protein, functionally interact during spliceosome assembly in yeast

      Vaijayanti C. Vaidya Usha Vijayraghavan

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      Earlier studies on genetic suppression ofprp24-1 byprp21-2 suggested an association between yeast Prp21 and Prp24 proteins, which are associated, respectively, with U2 snRNA and U6 snRNA. Here we report analyses of physical and functional interaction between these factors. Missense mutations in functionally important domains reside inprp21-2 andprp24-1. Two-hybrid assays do not detect interaction between wild-type or mutant proteins. Prp21-2 and Prp24-1 protein inprp21-2 orprp24-1 extracts can be heat-inactivatedin vitro. In contrast, heat-treated extracts from the revertant strainprp21-2 prp24-1 demonstrate allele-specific restoration of splicing. Suppression ofprp24-1 byprp21-2 does not cause coimmunoprecipitation of U2 and U6 snRNAs. We demonstrate the presence of Prp21 in the spliceosome assembly intermediate A2-1, and our data suggest the presence of Prp24 in the same complex. Kinetic analysis of assembly in heat-treated revertant extracts reveal a rate-limiting conversion of complex B to A2-1, suggesting transient association between the mutant proteins at this step. Our data also imply a requirement for Prp21 during B to A2-1 conversion. We conclude that a transient yet likely functional association between Prp21 and Prp24 occurs during spliceosome assembly.

    • A spectrum of genes expressed during early stages of rice panicle and flower development

      Kumuda M. Kushalappa Autar K. Mattoo Usha Vijayraghavan

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      To unravel gene expression patterns during rice inflorescence development, particularly at early stages of panicle and floral organ specification, we have characterized random cloned cDNAs from developmental-stage-specific libraries. cDNA libraries were constructed from rice panicles at the stage of branching and flower primordia specification or from panicles undergoing floral organogenesis. Partial sequence analysis and expression patterns of some of these random cDNA clones from these two rice panicle libraries are presented. Sequence comparisons with known DNA sequences in databases reveal that approximately sixtyeight per cent of these expressed rice genes show varying degrees of similarity to genes in other species with assigned functions. In contrast, thirtytwo per cent represent uncharacterized genes. cDNAs reported here code for potential rice homologues of housekeeping molecules, regulators of gene expression, and signal transduction molecules. They comprise both single-copy and multicopy genes, and genes expressed differentially, both spatially and temporally, during rice plant development. New rice cDNAs requiring specific mention are those with similarity toCOP1, a regulator of photomorphogenesis inArabidopsis; sequence-specific DNA binding plant proteins like AP2-domain-containing factors; genes that specify positional information in shoot meristems like leucine-rich-repeat-containing receptor kinases; regulators of chromatin structure like Polycomb domain protein; and also proteins induced by abiotic stresses.

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