Baynton C E, Potthoff S J, McCullough A J, Schuler M A
Department of Plant Biology, University of Illinois, Urbana 61801, USA.
Plant J. 1996 Oct;10(4):703-11. doi: 10.1046/j.1365-313x.1996.10040703.x.
The process of 5' and 3' splice site definition in plant pre-mRNA splicing differs from that in mammals and yeast. In mammals, splice sites are chosen by their complementarity to U1 snRNA surrounding the /GU at the 5' splice site and by the strength of the pyrimidine tract preceding the AG/ at the 3' splice site; in plants, the 3' intron boundary is defined in a position-dependent manner relative to AU-rich elements within the intron. To determine if uridines are utilized to any extent in plant 3' splice site recognition, uridines in the region preceding the normal (-1) 3' splice site of pea rbcS3A intron 1 were replaced with adenosines. This mutant activates two cryptic 3' splice sites (+62, +95) in the downstream exon, indicating that the uridines in the region immediately preceding the normal (-1) site are essential for recognition. Placement of different length uridine tracts upstream from the cryptic +62 site indicated that a cryptic exonic 3' splice site containing 14 or 10 uridine tracts with a G at -4 can effectively outcompete the normal 3' splice site containing an eight uridine tract with a U at -4. Substitutions at the -4 position demonstrated that the identity of the nucleotide at this position greatly affects 3' splice site selection. It has been concluded that several factors affect competition between these 3' splice sites. These factors include the position of the AU transition point, the strength of the uridine tract immediately preceding the 3' terminal CAG/ and the identity of nucleotide -4.
植物前体mRNA剪接中5'和3'剪接位点的定义过程与哺乳动物和酵母不同。在哺乳动物中，剪接位点是根据它们与5'剪接位点/GU周围的U1 snRNA的互补性以及3'剪接位点AG/之前嘧啶序列的强度来选择的；在植物中，3'内含子边界是相对于内含子内富含AU的元件以位置依赖的方式定义的。为了确定尿苷在植物3'剪接位点识别中是否有任何程度的利用，将豌豆rbcS3A内含子1正常（-1）3'剪接位点之前区域的尿苷替换为腺苷。这个突变体激活了下游外显子中的两个隐蔽3'剪接位点（+62，+95），表明正常（-1）位点之前紧邻区域的尿苷对于识别至关重要。在隐蔽的+62位点上游放置不同长度的尿苷序列表明，一个含有14个或10个尿苷序列且-4位为G的隐蔽外显子3'剪接位点能够有效地胜过含有8个尿苷序列且-4位为U的正常3'剪接位点。-4位的替换表明该位置核苷酸的身份极大地影响3'剪接位点的选择。已经得出结论，有几个因素影响这些3'剪接位点之间的竞争。这些因素包括AU转换点的位置、3'末端CAG/之前紧邻的尿苷序列的强度以及核苷酸-4的身份。
