Hoffman D C, Prescott D M
Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO 80309-0347, USA.
Nucleic Acids Res. 1997 May 15;25(10):1883-9. doi: 10.1093/nar/25.10.1883.
To learn about the evolution of internal eliminated segments (IESs) and gene scrambling in hypotrichous ciliates we determined the structure of the micronuclear (germline) gene encoding DNA polymerasealpha(DNA polalpha) in Oxytricha trifallax and compared it to the previously published structure of the germline DNA polalphagene in Oxytricha nova . The DNA polalphagene of O.trifallax contains 51 macronuclear-destined segments (MDSs) separated by 50 IESs, compared to 45 MDSs and 44 IESs in the O.nova gene. This means that IESs and MDSs have been gained and/or lost during evolutionary divergence of the two species. Most of the MDSs are highly scrambled in a similar non-random pattern in the two species. We present a model to explain how IESs, non-scrambled MDSs and scrambled MDSs may be added and/or eliminated during evolution. Corresponding IESs in the two species differ totally in sequence, and junctions between MDSs and IESs are shifted by 1-18 bp in O.trifallax compared to the O.nova gene. In both species a short region of the gene is distantly separated from the main part of the gene. Comparison of the gene in the two species shows that IESs and scrambling are highly malleable over evolutionary time.
为了了解寡毛纲纤毛虫内部消除片段（IESs）的进化以及基因重排情况，我们确定了三列尖毛虫中编码DNA聚合酶α（DNA polα）的微核（种系）基因的结构，并将其与之前发表的新尖毛虫种系DNA polα基因的结构进行了比较。三列尖毛虫的DNA polα基因包含51个注定进入大核的片段（MDSs），被50个IESs隔开，相比之下，新尖毛虫基因中有45个MDSs和44个IESs。这意味着在这两个物种的进化分歧过程中，IESs和MDSs有增减。在这两个物种中，大多数MDSs以相似的非随机模式高度重排。我们提出了一个模型来解释在进化过程中IESs、未重排的MDSs和重排的MDSs是如何添加和/或消除的。两个物种中相应的IESs在序列上完全不同，与新尖毛虫基因相比，三列尖毛虫中MDSs和IESs之间的连接点移动了1 - 18个碱基对。在这两个物种中，基因的一个短区域与基因的主要部分相距甚远。对这两个物种中该基因的比较表明，在进化过程中IESs和重排具有高度的可塑性。
