g Numerous RNA binding proteins are deposited onto an mRNA transcript to modulate posttranscriptional processing events ensuring proper mRNA maturation. Defining the interplay between RNA binding proteins that couple mRNA biogenesis events is crucial for understanding how gene expression is regulated. To explore how RNA binding proteins control mRNA processing, we investigated a role for the evolutionarily conserved polyadenosine RNA binding protein, Nab2, in mRNA maturation within the nucleus. This study reveals that nab2 mutant cells accumulate intron-containing pre-mRNA in vivo. We extend this analysis to identify genetic interactions between mutant alleles of nab2 and genes encoding a splicing factor, MUD2, and RNA exosome, RRP6, with in vivo consequences of altered pre-mRNA splicing and poly(A) tail length control. As further evidence linking Nab2 proteins to splicing, an unbiased proteomic analysis of vertebrate Nab2, ZC3H14, identifies physical interactions with numerous components of the spliceosome. We validated the interaction between ZC3H14 and U2AF2/U2AF 65 . Taking all the findings into consideration, we present a model where Nab2/ZC3H14 interacts with spliceosome components to allow proper coupling of splicing with subsequent mRNA processing steps contributing to a kinetic proofreading step that allows properly processed mRNA to exit the nucleus and escape Rrp6-dependent degradation.
Gene expression is temporally and spatially regulated to produce a precise protein expression profile that dictates the function of each cell. Although much of this control occurs at the level of transcription, both co-and posttranscriptional events also play key regulatory roles. Newly synthesized mRNAs undergo numerous processing events, including 5= capping, splicing, 3=-end processing, and export to the cytoplasm (1, 2). Ensuring the synchrony of mRNA biogenesis requires RNA binding proteins that not only perform the processing tasks but also couple the events to ensure that only properly processed mRNAs are available for translation in the cytoplasm (3).Key processing events that must be coordinated include splicing and 3=-end processing. Although steps in mRNA processing are often depicted and studied as separate events, there is a growing body of evidence that these processing events are intimately coupled to one another (2). For example, splicing and 3=-end processing are coupled in humans as mutations in splice site and polyadenylation consensus sequences mutually disrupt both splicing and polyadenylation (4-6). In addition, a number of splicing factors copurify with the 3=-end processing complex (7-10). For example, there is evidence that the splicing factor U2AF2/ U2AF 65 functions as a bridge between the U2 snRNP and the 3=-end processing machinery (11,12). Given the extensive coupling between RNA processing steps, it is important to consider the consequences when one step of the process is disrupted in vivo. Cells have developed numerous overlapping mechanisms to ensure that faulty mRNA transcripts are not...
Trichoderma reesei RUT-C30 is a well-known high-yielding cellulase-producing fungal strain that converts lignocellulose into cellulosic sugar for resource regeneration. Calcium is a ubiquitous secondary messenger that regulates growth and cellulase production in T. reesei. We serendipitously found that adding Sr2+ to the medium significantly increased cellulase activity in the T. reesei RUT-C30 strain and upregulated the expression of cellulase-related genes. Further studies showed that Sr2+ supplementation increased the cytosolic calcium concentration and activated the calcium-responsive signal transduction pathway of Ca2+–calcineurin-responsive zinc finger transcription factor 1 (CRZ1). Using the plasma membrane Ca2+ channel blocker, LaCl3, we demonstrated that Sr2+ induces cellulase production via the calcium signaling pathway. Supplementation with the corresponding concentrations of Sr2+ also inhibited colony growth. Sr2+ supplementation led to an increase in intracellular reactive oxygen species (ROS) and upregulated the transcriptional levels of intracellular superoxide dismutase (sod1) and catalase (cat1). We further demonstrated that ROS content was detrimental to cellulase production, which was alleviated by the ROS scavenger N-acetyl cysteine (NAC). This study demonstrated for the first time that Sr2+ supplementation stimulates cellulase production and upregulates cellulase genes via the calcium signaling transduction pathway. Sr2+ leads to an increase in intracellular ROS, which is detrimental to cellulase production and can be alleviated by the ROS scavenger NAC. Our results provide insights into the mechanistic study of cellulase synthesis and the discovery of novel inducers of cellulase.
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