The yeast Hrq1 protein is an important model for studying the human RECQL4 helicase and RECQL4-associated diseases. In this study, we simultaneously isolated and characterized two stable oligomeric states of Hrq1 expressed in insect cells: a monomeric form (Hrq1mon) and a higher-order oligomeric fraction (Hrq1-oligo). Intriguingly, ATP not only promotes the dissociation of the oligomeric fraction into monomeric or smaller Hrq1-containing species but also markedly stimulates the DNA-unwinding activities of both forms. Furthermore, Hrq1-mediated unwinding is strictly dependent on a forked DNA substrate, and its activity increases with increasing lengths of either the 5'- or 3'-single-stranded DNA tail. Based on the limited unwinding processivity of Hrq1, we propose a "relay-style" mechanism in which an initial Hrq1 monomer partially unwinds the duplex and subsequently dissociates, allowing additional Hrq1 monomers to bind the newly exposed 3' single-stranded region and continue the unwinding reaction. However, this process can be inhibited by ScRPA through competition for the exposed single-stranded DNA. These findings provide new insights into the oligomeric-state-dependent regulation and unwinding mechanism of Hrq1 and may contribute to a broader understanding of RecQ family helicases.

• PMID: 42567513
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Journal Article

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Zhu X, Dai Y, Xie Y, Guo H, Wang Z, Zhao H, Wang Z, Zhang Y, Liu Y, Zhang B

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