Uchida Naoyuki, Hoshino Shin-Ichi, Katada Toshiaki
Department of Physiological Chemistry, Graduate School of Pharmaceutical Sciences, University of Tokyo, Tokyo 113-0033, Japan.
J Biol Chem. 2004 Jan 9;279(2):1383-91. doi: 10.1074/jbc.M309125200. Epub 2003 Oct 28.
The poly(A) tail shortening in mRNA, called deadenylation, is the first rate-limiting step in eukaryotic mRNA turnover, and the polyadenylate-binding protein (PABP) appears to be involved in the regulation of this step. However, the precise role of PABP remains largely unknown in higher eukaryotes. Here we identified and characterized a human PABP-dependent poly(A) nuclease (hPAN) complex consisting of catalytic hPan2 and regulatory hPan3 subunits. hPan2 has intrinsically a 3' to 5' exoribonuclease activity and requires Mg2+ for the enzyme activity. On the other hand, hPan3 interacts with PABP to simulate hPan2 nuclease activity. Interestingly, the hPAN nuclease complex has a higher substrate specificity to poly(A) RNA upon its association with PABP. Consistent with the roles of hPan2 and hPan3 in mRNA decay, the two subunits exhibit cytoplasmic co-localization. Thus, the human PAN complex is a poly(A)-specific exoribonuclease that is stimulated by PABP in the cytoplasm.
信使核糖核酸（mRNA）中的聚腺苷酸尾缩短，即去腺苷酸化，是真核生物mRNA周转的首个限速步骤，聚腺苷酸结合蛋白（PABP）似乎参与了这一步骤的调控。然而，在高等真核生物中，PABP的确切作用在很大程度上仍不明确。在此，我们鉴定并表征了一种人源PABP依赖性聚腺苷酸核酸酶（hPAN）复合物，它由催化性的hPan2和调节性的hPan3亚基组成。hPan2本质上具有3'至5'外切核糖核酸酶活性，且酶活性需要Mg2+。另一方面，hPan3与PABP相互作用以模拟hPan2核酸酶活性。有趣的是，hPAN核酸酶复合物与PABP结合后对聚腺苷酸RNA具有更高的底物特异性。与hPan2和hPan3在mRNA降解中的作用一致，这两个亚基在细胞质中共定位。因此，人源PAN复合物是一种聚腺苷酸特异性外切核糖核酸酶，在细胞质中受PABP刺激。
