Blumenthal Thomas, Davis Paul, Garrido-Lecca Alfonso
Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO 80309 USA.
WormBook. 2015 Apr 28:1-20. doi: 10.1895/wormbook.1.175.1.
Nearly 15% of the ~20,000 C. elegans genes are contained in operons, multigene clusters controlled by a single promoter. The vast majority of these are of a type where the genes in the cluster are ~100 bp apart and the pre-mRNA is processed by 3' end formation accompanied by trans-splicing. A spliced leader, SL2, is specialized for operon processing. Here we summarize current knowledge on several variations on this theme including: (1) hybrid operons, which have additional promoters between genes; (2) operons with exceptionally long (> 1 kb) intercistronic regions; (3) operons with a second 3' end formation site close to the trans-splice site; (4) alternative operons, in which the exons are sometimes spliced as a single gene and sometimes as two genes; (5) SL1-type operons, which use SL1 instead of SL2 to trans-splice and in which there is no intercistronic space; (6) operons that make dicistronic mRNAs; and (7) non-operon gene clusters, in which either two genes use a single exon as the 3' end of one and the 5' end of the next, or the 3' UTR of one gene serves as the outron of the next. Each of these variations is relatively infrequent, but together they show a remarkable variety of tight-linkage gene arrangements in the C. elegans genome.
在约20,000个秀丽隐杆线虫基因中，近15%包含在操纵子中，即由单个启动子控制的多基因簇。其中绝大多数属于基因簇中的基因相隔约100个碱基对，前体mRNA通过3'端形成并伴随反式剪接进行加工的类型。一个剪接引导序列SL2专门用于操纵子加工。在此，我们总结了关于这一主题的几种变体的现有知识，包括：（1）杂合操纵子，其基因之间有额外的启动子；（2）具有超长（>1 kb）基因间区域的操纵子；（3）在靠近反式剪接位点处有第二个3'端形成位点的操纵子；（4）可变操纵子，其中外显子有时作为单个基因进行剪接，有时作为两个基因进行剪接；（5）SL1型操纵子，其使用SL1而非SL2进行反式剪接且不存在基因间间隔；（6）产生双顺反子mRNA的操纵子；以及（7）非操纵子基因簇，其中要么两个基因使用单个外显子作为一个基因的3'端和下一个基因的5'端，要么一个基因的3'非翻译区作为下一个基因的外显子。这些变体中的每一种都相对少见，但它们共同展示了秀丽隐杆线虫基因组中紧密连锁基因排列的显著多样性。
