Bhattacharya Sudha
Department of Biology, Ashoka University, Sonipat, Haryana, India.
Front Mol Biosci. 2023 Jun 8;10:1212082. doi: 10.3389/fmolb.2023.1212082. eCollection 2023.
is the causative agent of amoebiasis. DNA replication studies in first started with the ribosomal RNA genes located on episomal circles. Unlike most plasmids, rDNA circles lacked a fixed origin. Replication initiated from multiple sites on the episome, and these were preferentially used under different growth conditions. In synchronized cells the early origins mapped within the rDNA transcription unit, while at later times an origin in the promoter-proximal upstream intergenic spacer was activated. This is reminiscent of eukaryotic chromosomal replication where multiple potential origins are used. Biochemical studies on replication and recombination proteins in picked up momentum once the genome sequence was available. Sequence search revealed homologs of DNA replication and recombination proteins, including meiotic genes. The replicative DNA polymerases identified included the α, δ, of polymerase family B; lesion repair polymerases Rev1 and Rev3; a translesion repair polymerase of family A, and five families of polymerases related to family B2. Biochemical analysis of EhDNApolA confirmed its polymerase activity with expected kinetic constants. It could perform strand displacement, and translesion synthesis. The purified EhDNApolB2 had polymerase and exonuclease activities, and could efficiently bypass some types of DNA lesions. The single DNA ligase (EhDNAligI) was similar to eukaryotic DNA ligase I. It was a high-fidelity DNA ligase, likely involved in both replication and repair. Its interaction with EhPCNA was also demonstrated. The recombination-related proteins biochemically characterized were EhRad51 and EhDmc1. Both shared the canonical properties of a recombinase and could catalyse strand exchange over long DNA stretches. Presence of Dmc1 indicates the likelihood of meiosis in this parasite. Direct evidence of recombination in was provided by use of inverted repeat sequences located on plasmids or chromosomes. In response to a variety of stress conditions, and during encystation in recombination-related genes were upregulated and homologous recombination was enhanced. These data suggest that homologous recombination could have critical roles in trophozoite growth and stage conversion. Availability of biochemically characterized replication and recombination proteins is an important resource for exploration of novel anti-amoebic drug targets.
是阿米巴病的病原体。对其的DNA复制研究最初是从位于游离环上的核糖体RNA基因开始的。与大多数质粒不同，rDNA环缺乏固定的起始位点。复制从游离环上的多个位点起始，并且在不同的生长条件下这些位点被优先使用。在同步化细胞中，早期起始位点定位于rDNA转录单元内，而在较晚时候，启动子近端上游基因间隔区内的一个起始位点被激活。这让人联想到真核染色体复制，其中使用了多个潜在的起始位点。一旦基因组序列可用，对其复制和重组蛋白的生化研究便蓬勃开展起来。序列搜索揭示了DNA复制和重组蛋白的同源物，包括减数分裂基因。鉴定出的复制性DNA聚合酶包括B族聚合酶的α、δ；损伤修复聚合酶Rev1和Rev3；A族的一种跨损伤修复聚合酶，以及与B2族相关的五个聚合酶家族。对EhDNApolA的生化分析证实了其具有预期动力学常数的聚合酶活性。它可以进行链置换和跨损伤合成。纯化的EhDNApolB2具有聚合酶和核酸外切酶活性，并且可以有效地绕过某些类型的DNA损伤。单一的DNA连接酶（EhDNAligI）与真核DNA连接酶I相似。它是一种高保真DNA连接酶，可能参与复制和修复过程。还证实了它与EhPCNA的相互作用。经生化表征的与重组相关的蛋白是EhRad51和EhDmc1。两者都具有重组酶的典型特性，并且可以催化长DNA片段上的链交换。Dmc1的存在表明该寄生虫存在减数分裂的可能性。通过使用位于质粒或染色体上的反向重复序列，提供了其重组的直接证据。在应对各种应激条件时，以及在其包囊化过程中，与重组相关的基因上调，同源重组增强。这些数据表明同源重组可能在滋养体生长和阶段转换中起关键作用。具有生化表征的复制和重组蛋白的可用性是探索新型抗阿米巴药物靶点的重要资源。
