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The AG Dinucleotide Terminating Introns Is Important but Not Always Required for Pre-mRNA Splicing in the Maize Endosperm1
Program in Plant Molecular and Cellular Biology and Horticultural Sciences, 1143 Fifield Hall, P.O. Box 110690, University of Florida, Gainesville, Florida 32611-0690 Previous RNA analysis of lesions within the 15 intron-containing Sh2 (shrunken2) gene of maize (Zea mays) revealed that the majority of these mutants affect RNA splicing. Here we decipher further two of these mutants, sh2-i (shrunken2 intermediate phenotype) and sh2-7460. Each harbors a G-to-A transition in the terminal nucleotide of an intron, hence destroying the invariant AG found at the terminus of virtually all nuclear introns. Consequences of the mutations, however, differ dramatically. In sh2-i the mutant site is recognized as an authentic splice site in approximately 10% of the primary transcripts processed in the maize endosperm. The other transcripts exhibited exon skipping and lacked exon 3. A G-to-A transition in the terminus of an intron was also found in the mutant sh2-7460, in this case intron 12. The lesion activates a cryptic acceptor site downstream 22 bp within exon 13. In addition, approximately 50% of sh2-7460 transcripts contain intron 2 and 3 sequences. 1 This research was supported in part by the National Science Foundation (grant nos. IBN-9316887 and MCB-9420422) and by the U.S. Department of Agriculture Competitive Grants Program (grant nos. 94-37300-453, 97-36306-4461, 95-37301-2080, and 98-01006). This is Florida Agricultural Experiment Station journal series no. R-06349. 2 These authors contributed equally to the paper. * Corresponding author; e-mail hannah@gnv.ifas.ufl; fax 1-352-392-5653.
Plant Physiol. (1999) 120: 65-72
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