Prescott D M
Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder 80309-0347, USA.
J Eukaryot Microbiol. 1998 Nov-Dec;45(6):575-81. doi: 10.1111/j.1550-7408.1998.tb04552.x.
Hypotrichs have evolved extraordinary ways of organizing, manipulating, and replicating the DNA in their micronuclear and macronuclear genomes. Short macronuclear DNA molecules containing single genes are created by excision from chromosomes, accompanied by massive elimination of the germline DNA sequences between genes. Germline genes themselves are interrupted by multiple noncoding segments called internal eliminated segments, or IESs, that divide genes into multiple macronuclear-destined segments, or MDSs. The functional significance of this organization is unknown. Over evolutionary time IESs accumulate mutations rapidly, are inserted into or excised from genes, and shift position along DNA molecules. MDSs are ligated to create functional genes when IESs are spliced out of micronuclear DNA during macronuclear development. MDSs in some germline genes are in scrambled disorder and become unscrambled in association with IES elimination. Replication of DNA in the macronucleus is accomplished by organization of replication enzymes and factors into a structure that sweeps through the macronucleus to replicate the many millions of gene-sized DNA molecules. The significance of many of the bizarre DNA phenomena in the evolutionary/functional success of hypotrichs is still unclear.
纤毛虫已经进化出了非凡的方式来组织、操纵和复制其微核和大核基因组中的DNA。含有单个基因的短的大核DNA分子是通过从染色体上切除而产生的，同时伴随着基因间种系DNA序列的大量消除。种系基因本身被多个称为内部消除片段（IESs）的非编码片段打断，这些片段将基因分成多个大核定向片段（MDSs）。这种组织方式的功能意义尚不清楚。在进化过程中，IESs迅速积累突变，插入或从基因中切除，并沿着DNA分子移动位置。在大核发育过程中，当IESs从微核DNA中剪接出来时，MDSs被连接起来形成功能基因。一些种系基因中的MDSs处于混乱无序状态，并在IES消除时变得有序。大核中DNA的复制是通过将复制酶和因子组织成一种结构来完成的，这种结构在大核中穿梭以复制数百万个基因大小的DNA分子。许多奇异的DNA现象在纤毛虫进化/功能成功中的意义仍不清楚。
