Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, UK.
Department of Molecular Biology, Radboud University, Geert Grooteplein 26-28, 6525 GA Nijmegen, The Netherlands.
Nucleic Acids Res. 2023 Apr 11;51(6):2709-2724. doi: 10.1093/nar/gkad093.
The malaria parasite Plasmodium falciparum replicates via schizogony: an unusual type of cell cycle involving asynchronous replication of multiple nuclei within the same cytoplasm. Here, we present the first comprehensive study of DNA replication origin specification and activation during Plasmodium schizogony. Potential replication origins were abundant, with ORC1-binding sites detected every ∼800 bp. In this extremely A/T-biased genome, the sites were biased towards areas of higher G/C content, and contained no specific sequence motif. Origin activation was then measured at single-molecule resolution using newly developed DNAscent technology: a powerful method of detecting replication fork movement via base analogues in DNA sequenced on the Oxford Nanopore platform. Unusually, origins were preferentially activated in areas of low transcriptional activity, and replication forks also moved fastest through lowly transcribed genes. This contrasts with the way that origin activation is organised in other systems, such as human cells, and suggests that P. falciparum has evolved its S-phase specifically to minimise conflicts between transcription and origin firing. This may be particularly important to maximise the efficiency and accuracy of schizogony, with its multiple rounds of DNA replication and its absence of canonical cell-cycle checkpoints.
这是一种不同寻常的细胞周期类型，涉及同一细胞质内多个核的异步复制。在这里，我们首次对疟原虫裂殖生殖过程中的 DNA 复制起点指定和激活进行了全面研究。潜在的复制起点非常丰富，在每 800bp 左右检测到 ORC1 结合位点。在这个极度 A/T 偏倚的基因组中，这些位点偏向于具有更高 GC 含量的区域，并且没有特定的序列基序。然后，我们使用新开发的 DNAscent 技术在单分子分辨率下测量了起始激活：这是一种通过在牛津纳米孔平台上测序的 DNA 中的碱基类似物来检测复制叉运动的强大方法。不同寻常的是，复制起点优先在转录活性低的区域被激活，并且复制叉在转录活性低的基因中移动得最快。这与其他系统（如人类细胞）中起始激活的组织方式形成对比，表明恶性疟原虫已经专门进化了其 S 期，以最大程度地减少转录和起始点火之间的冲突。这对于最大限度地提高裂殖生殖的效率和准确性可能尤为重要，因为裂殖生殖具有多轮 DNA 复制，并且缺乏典型的细胞周期检查点。
