RESUMO
The multiprotein complexes involved in active dis-ruption of chromatin structure, homologous to yeast SWI/SNF complex, have been described for human and Drosophila cells. In all SWI/SNF-class complexes characterised so far, one of the key components is the SNF5-type protein. Here we describe the isolation of a plant (Arabidopsis thaliana ) cDNA encoding a 27 kDa protein which we named BSH, with high homology to yeast SNF5p and its human (INI1) and Drosophila (SNR1) counterparts as well as to other putative SNF5-type proteins from Caenorhabditis elegans, fish and yeast. With 240 amino acids, the Arabidopsis BSH is the smallest SNF5-type protein so far identified. When expressed in Saccharomyces cerevisiae, the gene for BSH partially complements the snf5 mutation. BSH is, however, unable to activate transcription in yeast when tethered to DNA. The gene for BSH occurs in single copy in the Arabidopsis genome and is ubiquitously expressed in the plant. Analysis of the whole cell and nuclear protein extracts with antibodies against recombinant BSH indicates that the protein is localised in nuclei. Transgenic Arabidopsis plants with markedly decreased physiological level of the BSH mRNA, resulting from the expression of antisense messenger, are viable but exhibit a distinctive phenotype characterised by bushy growth and flowers that are unable to produce seeds.
Assuntos
Proteínas de Arabidopsis , Arabidopsis/genética , Proteínas de Ligação a DNA/genética , Proteínas de Drosophila , Proteínas de Plantas/genética , Fatores de Transcrição/genética , Sequência de Aminoácidos , Animais , Sequência de Bases , Proteínas Cromossômicas não Histona , DNA de Plantas , Drosophila , Eletroforese em Gel de Poliacrilamida , Dosagem de Genes , Genes de Plantas , Humanos , Dados de Sequência Molecular , Família Multigênica , Mutagênese , Fenótipo , Proteínas de Plantas/metabolismo , Plantas Geneticamente Modificadas , RNA Mensageiro , RNA de Plantas , Coelhos , Proteína SMARCB1 , Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae , Homologia de Sequência de Aminoácidos , Fatores de Transcrição/metabolismo , Ativação Transcricional , Ubiquitinas/metabolismoRESUMO
The binding properties of the SPXK- and APXK-type peptides to the AT-rich DNA fragments of different length were studied by measuring the competition of peptides with Hoechst 33258 dye for DNA binding and by the gel shift assay analysis. In parallel to the experimental studies, molecular modeling techniques were used to analyze possible binding modes of the SPXZ and APXK motifs to the AT-rich DNA. The results of the competition measurements and gel shift assays suggest that serine at the i-1 position (i is proline) can be replaced by alanine without affecting the binding properties of the motif. Thus, the presence of the conserved serine in this motif in many DNA-binding proteins is probably not dictated by structural requirements. Based on the results of molecular modeling studies we propose that the binding mode of the SPXK-type motifs to the AT-rich DNA resembles closely that between the N-terminal arm of the homeodomain and DNA. This model confirms that serine in the SPXK motifs is not essential for the DNA binding. The model also indicates that if X in the motif is glutamic acid, this residue is probably protonated in the complex with DNA.
