Okagaki R J, Sullivan T D, Schiefelbein J W, Nelson O E
Laboratory of Genetics, University of Wisconsin, Madison 53706.
Plant Cell. 1992 Nov;4(11):1453-62. doi: 10.1105/tpc.4.11.1453.
The defective Suppressor-mutator (dSpm)-induced allele bronze1-mutable 13 (bz1-m13) and many of its derivative alleles are leaky mutants with measurable levels of flavonol O3-glucosyltransferase activity. This activity results from splicing at acceptor site-1, one of two cryptic 3' splice sites within the dSpm insertion in bz1-m13. In this study, splicing in bz1-m13 change-in-state (CS) alleles CS-3 and CS-64 was shown to be altered from bz1-m13; previous work found altered splicing in CS-9. CS-64 is a null allele and lacks the acceptor site-1-spliced transcript because this site is deleted. CS-3 and CS-9 had increased levels of the acceptor site-1 transcript relative to bz1-m13 and increased enzymic activities. A deletion in CS-9 altered splicing by eliminating acceptor site-2. Both acceptor sites were intact in CS-3, but a deletion removed most of a 275-bp GC-rich sequence in dSpm. This suggests that GC-rich sequences affect splicing and is consistent with models postulating a role for AU content in the splicing of plant introns. Splicing does not necessarily occur, however, at the junction of AU-rich intron sequences and GC-rich exon sequences.
缺陷抑制突变体（dSpm）诱导的等位基因青铜1-可变体13（bz1-m13）及其许多衍生等位基因是渗漏突变体，具有可测量水平的黄酮醇O3-葡萄糖基转移酶活性。这种活性源于在受体位点-1处的剪接，受体位点-1是bz1-m13中dSpm插入片段内两个隐蔽的3'剪接位点之一。在本研究中，bz1-m13状态改变（CS）等位基因CS-3和CS-64的剪接被证明与bz1-m13不同；先前的研究发现CS-9中存在剪接改变。CS-64是一个无效等位基因，缺乏受体位点-1剪接的转录本，因为该位点被删除了。相对于bz1-m13，CS-3和CS-9中受体位点-1转录本的水平增加，酶活性也增加。CS-9中的一个缺失通过消除受体位点-2改变了剪接。CS-3中的两个受体位点都是完整的，但一个缺失去除了dSpm中大部分275 bp富含GC的序列。这表明富含GC的序列影响剪接，并且与假设AU含量在植物内含子剪接中起作用的模型一致。然而，剪接不一定发生在富含AU的内含子序列和富含GC的外显子序列的交界处。
