ABSTRACT

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-3ʹ tails from degradation by 3ʹ exonucleases. LARP4 is a 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 in vivo but does not impair oligo(A) RNA binding by the purified recombinant La-module in vitro. 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.

摘要

在7种与La相关的蛋白中发现了称为La模块的蛋白结构域排列，包括La基序（LaM），连接子和RNA识别基序（RRM），分别是LARP1，LARP1B，LARP3（La蛋白），人类中的LARP4，LARP4B，LARP6和LARP7。几种LARPs在RNA代谢的特定方面具有独特的活性。La模块在链接器长度和RRM子类型的LARP之间有所不同。La蛋白和LARP7的La模块结合并保护带有UUU-3′尾巴的核RNA免受3′外切核酸酶的降解。LARP4是与poly（A）和胞质poly（A）结合蛋白PABPC1（也称为PABP）结合的mRNA poly（A）稳定因子。LARP1具有类似于LARP4的poly（A）长度保护和mRNA稳定作用。这里，我们表明，这些LARP1活性是由其La模块介导的，并且依赖于结合PABP的PAM2图案。LARP1的分离的La模块足以用于HEK293细胞中PABP依赖的poly（A）长度保护和mRNA稳定化。La模块中PAM2基序中的点突变损害mRNA稳定和PABP结合在体内但不影响纯化的重组La模块在体外对oligo（A）RNA的结合。我们表征了LARP1的异常PAM2序列，并表明它可能差异影响稳定和不稳定的mRNA。独特的LARP1 La模块可作为自主因子，赋予poly（A）保护和稳定异源mRNA。