Rabbit Anti-Human ASF/SF2 Polyclonal antibody

The splicing function of SR proteins is regulated by multisite phosphorylation of their C-terminal RS (arginine-serine rich) domains. SRPK1 has been shown to phosphorylate the prototype SR protein SRSF1 using a directional mechanism in which 11 serines flanked by arginines are sequentially fed from a docking groove in the large lobe of the kinase domain to the active site. Although this process is expected to operate on lengthy arginine serine repeats (>= 8), many SR proteins contain smaller repeats of only 1-4 dipeptides, raising the question of how alternate RS domain configurations are phosphorylated. To address this, we studied a splice variant of Tra2 beta that contains a C-terminal RS domain with short arginine serine repeats [Tra2 beta(Delta N)]. We showed that SRPK1 selectively phosphorylates several serines near the C-terminus of the RS domain. SRPK1 uses a distributive mechanism for Tra2 beta(Delta N) where the rate-limiting step is the dissociation of the protein substrate rather than nucleotide exchange as in the case of SRSF1. Although a functioning docking groove is required for efficient SRSF1 phosphorylation, this conserved structural element is dispensable for Tra2 beta(Delta N) phosphorylation. These large shifts in mechanism are likely to account for the slower net turnover rate of Tra2 beta(Delta N) compared to SRSF1 and may signal fundamental differences in phosphorylation among SR proteins with distinctive arginine serine profiles. Overall, these data indicate that SRPK1 conforms to changes in RS domain architecture using a flexible kinetic mechanism and selective usage of a conserved docking groove.

The maintenance of correct protein homeostasis ('proteostasis') is an essential activity of mammalian cells to preserve their vital properties and functions. Because of its importance, correct proteostasis is achieved by the cell in several ways and at several levels of each gene expression pathway. In many cases, mRNA-autoregulatory pathways based on a variety of feedback mechanisms have been observed to play a major role in keeping their concentration under control. This is especially true for RNA binding proteins because of their potential ability to bind their own pre-mRNA molecules, and in particular for two subsets of nuclear factors that are commonly referred to as heterogeneous ribonucleoproteins and serine-arginine-rich proteins. Regarding the mechanism, nonsense-mediated RNA degradation triggered by alternative splicing of their own messenger RNA is a very common autoregulation pathway to maintain constant expression levels within the cellular environment. Recently, however, alternative mechanisms other than nonsense-mediated decay have also been described to play a role for other RNA binding protein factors: serine-arginine-rich splicing factor 1 (SRSF1) and transactive response DNA binding protein 43 kDa (TDP-43). The aim of this minireview will be to discuss these old and new autoregulatory processes and their implication in disease development.