Human ras genes play central roles in coupling extracellular signals with complex intracellular networks controlling proliferation, differentiation, and apoptosis, among others processes. c-H-ras pre-mRNA can be alternatively processed into two mRNAs due to the inclusion or exclusion of the alternative exon IDX; this renders two proteins, p21H-Ras and p19H-RasIDX, which differ only at the carboxy terminus. Here, we have characterized some of the cis-acting sequences and trans-acting factors regulating IDX splicing. A downstream intronic silencer sequence (rasISS1), acting in concert with IDX, negatively regulates upstream intron splicing. This effect is mediated, at least in part, by the binding of hnRNP A1. Depletion and add-back experiments in nuclear extracts have confirmed hnRNP A1's inhibitory role in IDX splicing. Moreover, the addition of two SR proteins, SC35 and SRp40, can counteract this inhibition by strongly promoting the splicing of the upstream intron both in vivo and in vitro. Further, the RNA-dependent helicase p68 is also associated with both IDX and rasISS1 RNA, and suppression of p68 expression in HeLa cells by RNAi experiments results in a marked increase of IDX inclusion in the endogenous mRNA, suggesting a role for this protein in alternative splicing regulation.A common mechanism for gene expression regulation in metazoa is the use of alternative splice sites (SS) to produce multiple protein-coding sequences from the same pre-mRNA. It was recently predicted that nearly 60% of all human genes undergo at least one process of alternative splicing (41). The ever increasing known examples of alternative pre-mRNA processing are often tissue type or developmental state specific, indicating that complex regulation is involved in the selection of SS pairs (for a review, see reference 47). However, little is yet known about the detailed mechanisms regulating alternative splicing in mammalian cells.A number of RNA sequences that positively or negatively regulate the inclusion of alternative exons have been identified (12,22,24,26,32,35,38,42,61). Binding of certain sets of splicing factors to these regulatory sequences, together with the intrinsic strengths of the SS, dictates the specificity and efficiency of splicing, resulting in promotion or repression of each splicing event.The SR protein family is a well-characterized class of proteins involved in both constitutive and alternative splicing (29,58). Their mechanism of action involves binding to certain RNA sequences (commonly exonic enhancers) through their RNA recognition motifs and the recruitment of other splicing factors, stimulating the splicing efficiency of weak adjacent SS (1,30,33,56). SR protein binding to an exon is known to increase the binding of U2AF 65 to an upstream 3ЈSS (60) or that of U1 snRNP to a downstream 5ЈSS (6,27,36,39). SR proteins can also act in a RNA binding-independent way, promoting the assembly of general splicing factors in the proteinprotein network interactions that make up the mature spliceosome (5). Factors o...

Summary During the last decade, much has been learnt about the mechanisms by which oxidative stress is perceived by aerobic organisms. The Schizosaccharomyces pombe Pap1 protein is a transcription factor localized at the cytoplasm, which accumulates in the nucleus in response to different inducers, such as the pro‐oxidant hydrogen peroxide (H2O2) or the glutathione‐depleting agent diethylmaleate (DEM). As described for other H2O2 sensors, our genetic data indicates that H2O2 reversibly oxidizes two cysteine residues in Pap1 (Cys278 and Cys501). Surprisingly, our studies demonstrate that DEM generates a non‐reversible modification of at least two cysteine residues located in or close to the nuclear export signal of Pap1 (Cys523 and Cys532). This modification impedes the interaction of the nuclear exporter Crm1 with the nuclear export signal located at the carboxy‐terminal domain of Pap1. Mass spectrometry data suggest that DEM binds to the thiol groups of the target cysteine residues through the formation of a thioether. Here we show that DEM triggers Pap1 nuclear accumulation by a novel molecular mechanism.

In the last decade, proteomic technologies have been increasingly used in fish biology research. Proteomics has been applied primarily to investigate the physiology, development biology and the impact of contaminants in fish model organisms, such as zebrafish (Danio rerio), as well as in some commercial species produced in aquaculture, mainly salmonids and cyprinids. However, the lack of previous genetic information on most fish species has been a major drawback for a more general application of the different proteomic technologies currently available. Also, many teleosts of interest in biological research and with potential application in aquaculture hold unique physiological characteristics that cannot be directly addressed from the study of small laboratory fish models. This review describes proteomic approaches that have been used to investigate diverse biological questions in model and nonmodel fish species. We will also evaluate the current possibilities to integrate fish proteomics with other ''omic'' approaches, as well as with additional complementary techniques, in order to address the future challenges in fish biology research.