3'-Untranslated regions (3'UTRs) are recognized for their role in regulating mRNA turnover while the turnover of a specific group of mRNAs mediated by coding sequences (CDS) remains poorly understood. N4BP1 is a critical inflammatory regulator in vivo with a molecular mechanism that is not yet clearly defined. Our study reveals that N4BP1 efficiently degrades its mRNA targets via CDS rather than the 3'-UTR. This CDS-dependent mRNA turnover mechanism appears to be a general feature of N4BP1, as evidenced by testing multiple mRNA substrates, such as Fos-C, Fos-B, Jun-B and CXCL1. Detailed mapping of the motif identified a crucial 33nt (289-322) sequence near the 5'-end of Fos-C-CDS, where the presence of polyC is necessary for N4BP1-mediated degradation. Functional studies involving domain deletion and point mutations showed that both the KH and NYN domains are essential for N4BP1 to restrict mRNA substrates. The function of N4BP1 in mRNA turnover is not dependent on nonsense-mediated decay as it efficiently restricts mRNA substrates even in cells deficient in UPF1, UPF3A, and UPF3B. Additionally, the function of N4BP1 is not reliant on LUC7L3 despite its known association with this protein. Our findings suggest that N4BP1 acts as an endoribonuclease to degrade mRNA substrates primarily through coding sequences containing a C-rich motif.

中文翻译：

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NEDD4 结合蛋白 N4BP1 通过编码序列降解 mRNA 底物，而不受无义介导的衰变的影响。


3'-非翻译区 （3'UTR） 因其在调节 mRNA 周转中的作用而得到认可，而由编码序列 （CDS） 介导的特定一组 mRNA 的周转仍然知之甚少。N4BP1 是一种关键的体内炎症调节因子，其分子机制尚不清楚。我们的研究表明，N4BP1 通过 CDS 而不是 3'-UTR 有效降解其 mRNA 靶标。这种 CDS 依赖性 mRNA 周转机制似乎是 N4BP1 的一般特征，通过测试多种 mRNA 底物（如 Fos-C、Fos-B、Jun-B 和 CXCL1）可以证明。基序的详细定位在 Fos-C-CDS 的 5'-末端附近确定了一个关键的 33nt （289-322） 序列，其中 polyC 的存在是 N4BP1 介导的降解所必需的。涉及结构域缺失和点突变的功能研究表明，KH 和 NYN 结构域对于 N4BP1 限制 mRNA 底物至关重要。N4BP1 在 mRNA 周转中的功能不依赖于无义介导的衰变，因为它有效地限制了 mRNA 底物，即使在缺乏 UPF1、UPF3A 和 UPF3B 的细胞中也是如此。此外，尽管已知 N4BP1 与该蛋白相关，但 N4BP1 的功能并不依赖于 LUC7L3。我们的研究结果表明，N4BP1 作为核糖核酸内切酶，主要通过包含富含 C 的基序的编码序列降解 mRNA 底物。