Browsing by Author "Martínez, P"

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    Subset of hybrid eukaryotic proteins is exported by the type I secretion system of Erwinia chrysanthemi
    (2001) Palacios, JL; Zaror, I; Martínez, P; Uribe, F; Opazo, P; Socías, T; Gidekel, M; Venegas, A
    Erwinia chrysanthemi exports degradative enzymes by using a type I protein secretion system. The proteases secreted by this system lack an N-terminal signal peptide but contain a C-terminal secretion signal. To explore the substrate specificity of this system, we have expressed the E. chrysanthemi transporter system (prtDEF genes) in Escherichia coli and tested the ability of this ABC transporter to export hybrid proteins carrying C-terminal fragments off. chrysanthemi protease B. The C terminus contains six glycine-rich repeated motifs, followed by two repeats of the sequences DFLV and DW. Two types of hybrid proteins were assayed for transport, proteins with the 93-residue-protease-B C terminus containing one glycine rich repeat and both hydrophobic terminal repeats and proteins with the 181-residue C terminus containing all repeat motifs, Although the shorter C terminus is unable to export the hybrids, the longer C terminus can promote the secretion of hybrid proteins with N termini as large as 424 amino acids, showing that the glycine-rich motifs are required for the efficient secretion of these hybrids. However, the secretion of hybrids occurs only if these proteins do not carry disulfide bonds in their mature structures. These latter results suggest that disulfide bond formation can occur prior to or during the secretion. Disulfide bonds may prevent type I secretion of hybrids. One simple hypothesis to explain these results is that the type I channel is too narrow to permit the export of proteins with secondary structures stabilized by disulfide bonds.
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    Temporal and spatial variation in settlement of the gastropod Concholepas concholepas in natural and artificial substrata
    (2002) Martínez, P; Navarrete, SA
    Settlement of concholepas concholepas (Gastropoda: Muricidae) on natural and artificial substrata was studied between April 1999 and March 2001 at two sites in central Chile; the Las Cruces Marine Reserve and El Quisco Management and Exploited Area. Four different artificial materials were tested in the low intertidal zone during 1999 settlement season to determine their properties as settlement and microhabitat substrata for competent Concholepas larvae. Globular pads made of plastic filaments were identified as the best artificial collectors, exhibiting overall higher settlement rates than rock plots and lower variability among replicates within a given site. Thus, subsequent monitoring of settlement used only these globular pads that were replaced twice monthly, The temporal pattern of settlement was remarkably similar from year to year, starting at the end of austral winter (August-September) and ending in summer (December-January), defining a temporally restricted settlement season. Settlement at two sites within the Marine Reserve of Las Cruces was significantly higher than at sites in El Quisco. However, during the second settlement season, an additional site at El Quisco exhibited settlement rates comparable to those observed at Las Cruces. The results show that Concholepas settlement varies significantly over scales of several hundreds of metres as well as tens of kilometres, probably due to differences in coastal oceanographic conditions.
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    Temporal and spatial variation in the distribution of epineustonic competent larvae of Concholepas concholepas along the central coast of Chile
    (2002) Poulin, E; Palma, AT; Leiva, G; Hernández, E; Martínez, P; Navarrete, SA; Castilla, JC
    The abundance of competent epineustonic larvae of the gastropod Concholepas concholepas (Gastropoda: Muricidae) in nearshore waters at 2 sites along the central coast of Chile was examined through monthly plankton tows from July 1999 to June 2000, Larvae were found in plankton collections from July 1999 to February 2000 with maximum abundance in September and October. Settlement in artificial collectors deployed onshore on the lower intertidal zone showed the same unimodal pattern with a settlement peak during October and November. Variation in larval distribution among sampling dates was related to the occurrence of north-south winds. We found that C, concholepas larvae were more abundant closer to shore after moderate southerly wind periods than on calm days, probably because of the shoreward advection of the upper sea surface layer. While sampling during a strong coastal upwelling event (produced by strong southwesterly winds), C. concholepas larvae were only found in the upwelled waters between the front and the coast. This unusual pattern contrasts with what would be expected for typical epineustonic larvae, suggesting the existence of a mechanism of transport or retention by which C. concholepas larvae stay near coastal settling areas, thus avoiding offshore dispersion.