RESUMEN
The actin cytoskeleton plays a central part in the dynamic organization of eukaryotic cell structure. Nucleation of actin filaments is a crucial step in the establishment of new cytoskeletal structures or modification of existing ones, providing abundant targets for regulatory processes. A substantial part of our understanding of actin nucleation derives from studies on yeast and metazoan cells. However, recent advances in structural and functional genome analysis in less traditional models, such as plants or Dictyostelium discoideum, provide an emerging picture of an evolutionarily conserved core of at least two actin nucleation mechanisms, one mediated by the Arp2/3 complex and the other one by the formin-based module. A considerable degree of conservation is found also in the systems controlling the balance between filamentous and globular actin (profilin, actin-depolymerizing factor/cofilin) and even in certain regulatory aspects, such as the involvement of Rho-related small GTPases. Identification of such conserved elements provides a prerequisite for the characterization of evolutionarily variable aspects of actin regulation which may be responsible for the rich morphological diversity of eukaryotic cells.
Asunto(s)
Citoesqueleto de Actina/fisiología , Actinas/fisiología , Arabidopsis/fisiología , Dictyostelium/fisiología , Factores Despolimerizantes de la Actina , Proteína 2 Relacionada con la Actina , Actinas/genética , Actinas/ultraestructura , Animales , Arabidopsis/genética , Proteínas de Arabidopsis , Evolución Biológica , Proteínas Contráctiles/fisiología , Proteínas del Citoesqueleto/fisiología , Factores de Intercambio de Guanina Nucleótido/fisiología , Proteínas de Microfilamentos/fisiología , Modelos Biológicos , Profilinas , Proteínas de Unión al GTP rho/fisiologíaAsunto(s)
Proteínas de Arabidopsis/aislamiento & purificación , Arabidopsis/crecimiento & desarrollo , Proteínas Portadoras/aislamiento & purificación , Exocitosis/fisiología , Flores/crecimiento & desarrollo , Vesículas Secretoras/metabolismo , Arabidopsis/citología , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Proteínas Portadoras/genética , Proteínas Portadoras/metabolismo , ADN Complementario/análisis , ADN Complementario/genética , Flores/citología , Flores/metabolismo , Sustancias Macromoleculares , Filogenia , Proteínas de Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/aislamiento & purificación , Proteínas de Saccharomyces cerevisiae/metabolismo , Proteínas de Transporte VesicularAsunto(s)
Proteínas de Unión al Calcio/metabolismo , Miosinas/metabolismo , Fenómenos Fisiológicos de las Plantas , Ribonucleoproteínas/metabolismo , Secuencia de Aminoácidos , Señalización del Calcio , Calreticulina , Pared Celular/metabolismo , Datos de Secuencia Molecular , Miosinas/química , Homología de Secuencia de AminoácidoRESUMEN
BACKGROUND: The formin family of proteins has been implicated in signaling pathways of cellular morphogenesis in both animals and fungi; in the latter case, at least, they participate in communication between the actin cytoskeleton and the cell surface. Nevertheless, they appear to be cytoplasmic or nuclear proteins, and it is not clear whether they communicate with the plasma membrane, and if so, how. Because nothing is known about formin function in plants, I performed a systematic search for putative Arabidopsis thaliana formin homologs. RESULTS: I found eight putative formin-coding genes in the publicly available part of the Arabidopsis genome sequence and analyzed their predicted protein sequences. Surprisingly, some of them lack parts of the conserved formin-homology 2 (FH2) domain and the majority of them seem to have signal sequences and putative transmembrane segments that are not found in yeast or animals formins. CONCLUSIONS: Plant formins define a distinct subfamily. The presence in most Arabidopsis formins of sequence motifs typical or transmembrane proteins suggests a mechanism of membrane attachment that may be specific to plant formins, and indicates an unexpected evolutionary flexibility of the conserved formin domain.
Asunto(s)
Proteínas de la Membrana/química , Proteínas de Plantas/química , Secuencias de Aminoácidos , Secuencia de Aminoácidos , Arabidopsis/química , Arabidopsis/genética , Secuencia de Consenso , Proteínas de la Membrana/genética , Datos de Secuencia Molecular , Péptidos/química , Péptidos/clasificación , Péptidos/genética , Proteínas de Plantas/clasificación , Proteínas de Plantas/genética , Estructura Terciaria de Proteína , Alineación de Secuencia , Homología de Secuencia de AminoácidoRESUMEN
Rab GTPases play a central role in the control of vesicular membrane traffic. These proteins cycle between cytosolic and membrane-bound compartments in a guanine nucleotide-dependent manner, a process that is regulated by several accessory proteins. Of particular interest are the Rab guanosine nucleotide diphosphate dissociation inhibitor proteins (Rab-GDI) which bind to prenylated Rab GTPases, slow the rate of GDP dissociation and escort GDP bound Rab proteins to their target membranes and retrieve them after completion of their catalytic cycle. We have cloned from Arabidopsis thaliana a cDNA coding for the Rab guanosine diphosphate dissociation inhibitor (AtGDI1) by functional complementation of the Saccharomyces cerevisiae sec19-1 mutant. The Arabidopsis cDNA potentially encodes a 49850 Da protein which is homologous to yeast GDI (49%) and to other members of the Rab-GDI family (49-63%). Northern blot analysis indicates that the mRNA is expressed in all tissues examined. The existence of a plant homologue of the Rab-GDI family indicates that the basic vesicle traffic control machinery may be highly conserved in plants as it is in yeast and mammals.
Asunto(s)
ADN Complementario/genética , Proteínas de Unión al GTP/genética , Inhibidores de Disociación de Guanina Nucleótido , Mutación , Saccharomyces cerevisiae/genética , Secuencia de Aminoácidos , Arabidopsis/genética , Clonación Molecular , Dosificación de Gen , Prueba de Complementación Genética , Datos de Secuencia Molecular , Filogenia , ARN Mensajero/análisis , ARN de Planta/análisis , Alineación de Secuencia , Análisis de Secuencia de ADNRESUMEN
The yeast Ste20 protein kinase is involved in pheromone response. Mammalian homologs of Ste20 exist, but their function remains unknown. We identified a novel yeast STE20 homolog, CLA4, in a screen for mutations lethal in the absence of the G1 cyclins Cln1 and Cln2. Cla4 is involved in budding and cytokinesis and interacts with Cdc42, a GTPase required for polarized cell growth. Despite a cytokinesis defect, cla4 mutants are viable. However, double cla4 ste20 mutants cannot maintain septin rings at the bud neck and cannot undergo cytokinesis. Mutations in CDC12, which encodes one of the septins, were found in the same screen. Cla4 and Ste20 kinases apparently share a function in localizing cell growth with respect to the septin ring.
Asunto(s)
Proteínas Fúngicas/genética , Genes Fúngicos/genética , Proteínas Serina-Treonina Quinasas/genética , Proteínas Serina-Treonina Quinasas/fisiología , Proteínas de Saccharomyces cerevisiae , Levaduras/crecimiento & desarrollo , Secuencia de Aminoácidos , Compartimento Celular/fisiología , Proteínas de Ciclo Celular/genética , División Celular/fisiología , Polaridad Celular/fisiología , Ciclinas/genética , Ciclinas/metabolismo , GTP Fosfohidrolasas/metabolismo , Péptidos y Proteínas de Señalización Intracelular , Quinasas Quinasa Quinasa PAM , Datos de Secuencia Molecular , Feromonas/metabolismo , Proteína Quinasa C/metabolismo , Homología de Secuencia de Aminoácido , Transducción de Señal , Levaduras/enzimología , Levaduras/genéticaRESUMEN
Cyclin-dependent protein kinases have a central role in cell cycle regulation. In Saccharomyces cerevisiae, Cdc28 kinase and the G1 cyclins Cln1, 2 and 3 are required for DNA replication, duplication of the spindle pole body and bud emergence. These three independent processes occur simultaneously in late G1 when the cells reach a critical size, an event known as Start. At least one of the three Clns is necessary for Start. Cln3 is believed to activate Cln1 and Cln2, which can then stimulate their own accumulation by means of a positive feedback loop. They (or Cln3) also activate another pair of cyclins, Clb5 and 6, involved in initiating S phase. Little is known about the role of Clns in spindle pole body duplication and budding. We report here the isolation of a gene (CLA2/BUD2/ERC25) that codes for a homologue of mammalian Ras-associated GTPase-activating proteins (GAPs) and is necessary for budding only in cln1 cln2 cells. This suggests that Cln1 and Cln2 may have a direct role in bud formation.
Asunto(s)
Ciclo Celular , Ciclinas/fisiología , Proteínas Fúngicas/fisiología , Activadores de GTP Fosfohidrolasa , Proteínas/fisiología , Proteínas de Saccharomyces cerevisiae , Saccharomyces cerevisiae/citología , Secuencia de Aminoácidos , Secuencia de Bases , Clonación Molecular , GTP Fosfohidrolasas , Proteínas Activadoras de GTPasa , Genes Letales , Humanos , Recién Nacido , Datos de Secuencia Molecular , Alineación de Secuencia , Homología de Secuencia de Aminoácido , Tripeptidil Peptidasa 1 , Proteínas Activadoras de ras GTPasaAsunto(s)
Ciclo Celular/genética , Saccharomyces cerevisiae/citología , Schizosaccharomyces/citología , Ciclo Celular/fisiología , Ciclinas/genética , Retroalimentación , Regulación Fúngica de la Expresión Génica , Genes Fúngicos , Interfase/genética , Interfase/fisiología , Modelos Biológicos , Familia de Multigenes , Proteínas Quinasas/metabolismo , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Schizosaccharomyces/genética , Schizosaccharomyces/metabolismoRESUMEN
At the exponential growth phase, nystatin-treated Saccharomyces cerevisiae cells stain with Rhodamine B if they have not previously been exposed to killer toxin produced by Kluyveromyces lactis. This finding constitutes the principle of a method for estimating the activity of this toxin.