Intramural Research Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, United States.
Department of Biochemistry & Centre for Structural Biology, McGill University, Montreal, Canada.
RNA Biol. 2021 Feb;18(2):275-289. doi: 10.1080/15476286.2020.1860376. Epub 2020 Dec 23.
The protein domain arrangement known as the La-module, comprised of a La motif (LaM) followed by a linker and RNA recognition motif (RRM), is found in seven La-related proteins: LARP1, LARP1B, LARP3 (La protein), LARP4, LARP4B, LARP6, and LARP7 in humans. Several LARPs have been characterized for their distinct activity in a specific aspect of RNA metabolism. The La-modules vary among the LARPs in linker length and RRM subtype. The La-modules of La protein and LARP7 bind and protect nuclear RNAs with UUU-3' tails from degradation by 3' exonucleases. LARP4 is an mRNA poly(A) stabilization factor that binds poly(A) and the cytoplasmic poly(A)-binding protein PABPC1 (also known as PABP). LARP1 exhibits poly(A) length protection and mRNA stabilization similar to LARP4. Here, we show that these LARP1 activities are mediated by its La-module and dependent on a PAM2 motif that binds PABP. The isolated La-module of LARP1 is sufficient for PABP-dependent poly(A) length protection and mRNA stabilization in HEK293 cells. A point mutation in the PAM2 motif in the La-module impairs mRNA stabilization and PABP binding but does not impair oligo(A) RNA binding by the purified recombinant La-module . We characterize the unusual PAM2 sequence of LARP1 and show it may differentially affect stable and unstable mRNAs. The unique LARP1 La-module can function as an autonomous factor to confer poly(A) protection and stabilization to heterologous mRNAs.
已知的蛋白结构域排列方式被称为 La 模块，由 La 基序（LaM）、连接子和 RNA 识别基序（RRM）组成，存在于七种 La 相关蛋白中：人类的 LARP1、LARP1B、LARP3（La 蛋白）、LARP4、LARP4B、LARP6 和 LARP7。几种 LARPs 的特征在于它们在 RNA 代谢的特定方面具有独特的活性。La 模块在 LARPs 之间的差异在于连接子的长度和 RRM 亚型。La 蛋白和 LARP7 的 La 模块结合并保护具有 UUU-3' 尾巴的核 RNA 免受 3' 外切核酸酶的降解。LARP4 是一种 mRNA 多聚（A）稳定因子，可结合多聚（A）和细胞质多聚（A）结合蛋白 PABPC1（也称为 PABP）。LARP1 表现出与 LARP4 相似的多聚（A）长度保护和 mRNA 稳定性。在这里，我们表明这些 LARP1 活性由其 La 模块介导，并且依赖于结合 PABP 的 PAM2 基序。LARP1 的分离 La 模块足以在 HEK293 细胞中进行依赖 PABP 的多聚（A）长度保护和 mRNA 稳定。La 模块中的 PAM2 基序中的点突变会损害 mRNA 稳定性和 PABP 结合，但不会损害纯化重组 La 模块的寡聚（A）RNA 结合。我们对 LARP1 独特的 PAM2 序列进行了表征，并表明它可能对稳定和不稳定的 mRNA 产生不同的影响。独特的 LARP1 La 模块可以作为自主因子，赋予异源 mRNA 多聚（A）保护和稳定性。
