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More than 90% of human genes undergo a processing step called splicing, whereby non-coding introns are removed from initial transcripts and coding exons are ligated together to yield mature messenger RNA. Roughly 50% of human genetic diseases correspond to aberrant splicing. Splicing is catalyzed by an RNA/protein machine called the spliceosome. RNA components of the spliceosome are at least partly responsible for splicing catalysis. In addition, in vitro analyses implicate an essential and very highly conserved protein, Prp8, in orchestrating key steps in spliceosome assembly and possibly catalysis. Interestingly, mutant alleles of Prp8 are the cause of retinitis pigmentosa, an inherited form of retinal degeneration. A key goal is elucidation of the precise role of Prp8 in the spliceosome by high resolution structural analysis. The large size of Prp8 and its insolubility hinder progress in this regard. Instead, structural understanding of Prp8 can be gained by investigating domains in isolation; however there is only limited information as to what domain boundaries are and few hints about the functional relevance of putative domains. Here we have further defined the previously proposed domain IV in Prp8, and identified the domain IV core. Structural determination of the domain IV core reveals an RNase H fold, which could not be predicted based on primary sequence alone. RNase H recognizes A-form nucleic acid duplexes, which strongly suggests the domain IV core interacts with double-stranded RNA in the context of the spliceosome. Characterizing the binding preferences of the domain IV revealed the highest affinity is for a 4-helix junction structure adopted by the very RNAs at the spliceosome active site. Our characterization of the protein/RNA binding interface by complementary footprinting techniques currently provides the best model of how RNA interacts with an essential protein component at the heart of the spliceosome.

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Orientador: Eduardo Bagagli / Resumo: Os dermatófitos são um grupo de fungos constituídos pelos gêneros Trichophyton, Epidermophyton e Microsporum que têm a habilidade de degradar a queratina. É por essa razão que podem colonizar a pele do homem e dos animais, embora também possam crescer no ambiente, geralmente em solos com restos de queratina. As características morfológicas permitem a identificação e classificação taxonômica das espécies, mas realizar um diagnóstico baseado nestas características pode levar a erros. As técnicas moleculares ajudam a realizar diagnósticos mais rápidos baseados em uma identificação molecular e também têm possibilitado importantes avanços quanto aos estudos filogenéticos, sendo as sequências ITS1-5.8S-ITS2 as mais utilizadas. No entanto, estes marcadores não são suficientes para identificar e elucidar todas as relações filogenéticas e taxonômicas dos dermatófitos devido à ampla variedade de espécies existentes, -sendo necessário novos marcadores genéticos, como o intein PRP8. Os inteins são elementos genéticos parasitas, de natureza proteica, presentes em alguns fungos e estão associados a importantes genes altamente conservados. Ointein PRP8 está localizado nogenePRP8 que codifica para a proteína PRP8 associada ao complexo do spliciosoma. O presente estudo visa caracterizar o intein PRP8 em fungos dermatófitos, de forma a empregar estes elementos genéticos como marcadores moleculares para uma correta identificação destas espécies e elucidações das relações filogenéticas do grupo.... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Dermatophytes are a fungal group composed by the genera Trichophyton, Epidermophyton and Microsporum with the ability to degrade keratin. That is why they can colonize the skin of man and animals, although they can also grow in the environment, usually in soils with remains of keratin. The morphological characteristics allow the identification and taxonomic classification of the species, but a diagnosis based on these characteristics is difficult. Molecular techniques made diagnoses based on molecular identification faster and made possible important advances in phylogenetic studies, with ITS1-5.8s-ITS2 sequences being the most used. However, these markers are not enough to elucidate all the phylogenetic relationships and taxonomic of dermatophytes due to the wide variety of existing species, and new genetic markers may be needed for correct identification and phylogenetic studies, such as the PRP8 intein. Inteins are parasitic genetic elements of a protein nature present in some fungi and are associated with important highly conserved genes. The PRP8 intein is located within the PRP8 gene coding for the PRP8 protein associated with the spliciosome complex. The present study aims to characterize the PRP8 intein in dermatophyte fungi, in order to use these genetic elements as molecular markers for a correct identification of these species and elucidations of the phylogenetic relationships of the group. To accomplish this goal, 45 strains were molecularly characterized using th... (Complete abstract click electronic access below) / Mestre

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<p>Chromatin is a highly dynamic, regulatory component in the process of transcription, repair, recombination and replication. The BRG1 and SNF2H proteins are ATP-dependent chromatin remodeling proteins that modulate chromatin structure to regulate DNA accessibility for DNA-binding proteins involved in these processes. The BRG1 protein is a central ATPase of the SWI/SNF complexes involved in chromatin remodeling associated with regulation of transcription. SWI/SNF complexes are biochemically hetero-geneous but little is known about the unique functional characteristics of the various forms. We have shown that SWI/SNF activity in SW13 cells affects actin filament organization dependent on the RhoA signaling pathway. We have further shown that the biochemical composition of SWI/SNF complexes qualitatively affects the remodeling activity and that the composition of biochemically purified SWI/SNF complexes does not reflect the patterns of chromatin binding of individual subunits. Chromatin binding assays (ChIP) reveal variations among subunits believed to be constitutive, suggesting that the plasticity in SWI/SNF complex composition is greater than suspected. We have also discovered an interaction between BRG1 and the splicing factor Prp8, linking SWI/SNF activity to mRNA processing. We propose a model whereby parts of the biochemical heterogeneity is a result of function and that the local chromatin environment to which the complex is recruited affect SWI/SNF composition.</p><p>We have also isolated the novel B-WICH complex that contains WSTF, SNF2H, the splicing factor SAP155, the RNA helicase II/Guα, the transcription factor Myb-binding protein 1a, the transcription factor/DNA repair protein CSB and the RNA processing factor DEK. The formation of this complex is dependent on active transcription and links chromatin remodeling by SNF2H to RNA processing.</p><p>By linking chromatin remodeling complexes with RNA processing proteins our work has begun to build a bridge between chromatin and RNA, suggesting that factors in chromatin associated assemblies translocate onto the growing nascent RNA.</p>

Chromatin is a highly dynamic, regulatory component in the process of transcription, repair, recombination and replication. The BRG1 and SNF2H proteins are ATP-dependent chromatin remodeling proteins that modulate chromatin structure to regulate DNA accessibility for DNA-binding proteins involved in these processes. The BRG1 protein is a central ATPase of the SWI/SNF complexes involved in chromatin remodeling associated with regulation of transcription. SWI/SNF complexes are biochemically hetero-geneous but little is known about the unique functional characteristics of the various forms. We have shown that SWI/SNF activity in SW13 cells affects actin filament organization dependent on the RhoA signaling pathway. We have further shown that the biochemical composition of SWI/SNF complexes qualitatively affects the remodeling activity and that the composition of biochemically purified SWI/SNF complexes does not reflect the patterns of chromatin binding of individual subunits. Chromatin binding assays (ChIP) reveal variations among subunits believed to be constitutive, suggesting that the plasticity in SWI/SNF complex composition is greater than suspected. We have also discovered an interaction between BRG1 and the splicing factor Prp8, linking SWI/SNF activity to mRNA processing. We propose a model whereby parts of the biochemical heterogeneity is a result of function and that the local chromatin environment to which the complex is recruited affect SWI/SNF composition. We have also isolated the novel B-WICH complex that contains WSTF, SNF2H, the splicing factor SAP155, the RNA helicase II/Guα, the transcription factor Myb-binding protein 1a, the transcription factor/DNA repair protein CSB and the RNA processing factor DEK. The formation of this complex is dependent on active transcription and links chromatin remodeling by SNF2H to RNA processing. By linking chromatin remodeling complexes with RNA processing proteins our work has begun to build a bridge between chromatin and RNA, suggesting that factors in chromatin associated assemblies translocate onto the growing nascent RNA.