Structure and expression of a U1 snRNA gene from Arabidopsis thaliana

U1 snRNA is one of a group of spliceosomal snRNAs that function in the removal of introns from pre-mRNA. U1 snRNA is encoded by a small multigene family in Arabidopsis, consisting of between five and eight U1 genes. U1a snRNA is unique in having an extra U residue at position +2, which occurs in the region of U1 RNA which base pairs with the 5' splice site of introns. Mutations in this region have been shown to affect splicing, implying the sequence heterogeneity of U1a may have a functional significance. The promoter of U1a snRNA contains regulatory sequences previously described for other plant snRNAs: the CAAT box, $-$78 sequence, TATA box and 3' box. The U1a promoter also contains the octamer motif, a sequence element commonly found in vertebrate snRNA genes. In addition, U1a contains five sequence motifs repeated numerous times in the promoter. Three of these repeated sequences appear to be unique to the U1a gene. Two others resemble the Cauliflower Mosaic Virus 35S box II sequence and the AT box, which is found in light-regulated genes.U1a promoter deletion-gene fusion constructs using the reporter gene $\beta$-glucuronidase were used to discover whether U1a is expressed in a tissue-specific manner and to determine the minimal promoter length needed for transcription. The U1a-GUS chimeric gene is expressed at much higher levels in leaf tissue than in bud, flower or stem tissue. Expression of the U1a-GUS construct appears to be developmentally-regulated as well as light-regulated in tobacco leaves. This is the first report of differential expression of any plant snRNA gene.U of I OnlyETDs are only available to UIUC Users without author permissio