Snustad D P, Haas N A, Kopczak S D, Silflow C D
Department of Genetics and Cell Biology, University of Minnesota, St. Paul 55108-1095.
Plant Cell. 1992 May;4(5):549-56. doi: 10.1105/tpc.4.5.549.
The small genome of Arabidopsis contains at least nine expressed beta-tubulin (TUB) genes, in contrast to the large genomes of vertebrate animals, which contain a maximum of seven expressed beta-tubulin genes. In this study, we report the structures of seven new TUB genes (TUB2, TUB3, TUB5, TUB6, TUB7, TUB8, and TUB9) of Arabidopsis. The sequences of TUB1 and TUB4 had been reported previously. Sequence similarities and unique structural features suggest that the nine TUB genes evolved by way of three branches in the plant beta-tubulin gene evolutionary tree. Two genes (TUB2 and TUB3) encode the same beta-tubulin isoform; thus, the nine genes predict eight different beta-tubulins. In contrast to the alpha-tubulin (TUA) genes with their divergent intron patterns, all nine TUB genes contain 2 introns at conserved positions. Noncoding 3' gene-specific hybridization probes have been constructed for all nine TUB genes and used in RNA gel blot analyses to demonstrate that all nine genes are transcribed. Two-dimensional protein immunoblot analyses have resolved at least seven different beta-tubulin isoforms in Arabidopsis, indicating that most, if not all, of the TUB transcripts are translated.
拟南芥的小基因组至少包含9个表达的β-微管蛋白（TUB）基因，与之形成对比的是，脊椎动物的大基因组中最多含有7个表达的β-微管蛋白基因。在本研究中，我们报道了拟南芥7个新的TUB基因（TUB2、TUB3、TUB5、TUB6、TUB7、TUB8和TUB9）的结构。TUB1和TUB4的序列先前已有报道。序列相似性和独特的结构特征表明，这9个TUB基因在植物β-微管蛋白基因进化树中通过三个分支进化而来。两个基因（TUB2和TUB3）编码相同的β-微管蛋白异构体；因此，这9个基因预测有8种不同的β-微管蛋白。与具有不同内含子模式的α-微管蛋白（TUA）基因不同，所有9个TUB基因在保守位置都含有2个内含子。已为所有9个TUB基因构建了非编码3'基因特异性杂交探针，并用于RNA凝胶印迹分析，以证明所有9个基因都被转录。二维蛋白质免疫印迹分析已分辨出拟南芥中至少7种不同的β-微管蛋白异构体，这表明大多数（如果不是全部）TUB转录本都被翻译了。
