[en] The formation of the Schizosaccharomyces pombe cell wall requires the co-ordinated activity of enzymes involved in the biosynthesis and modification of its components, such as glucans. The ?-glucan-synthase complex synthesizes linear ?-1,3-glucans, which remain unorganized and alkali-soluble until covalent linkages are set up between ?-1,3-glucans and other cell wall components. Cell wall transferases using ?-1,3-glucans as substrates could perform important functions in the assembly and organization of the cell wall. Several proteins belonging to the glycoside hydrolase family 72 (GH72) with ?-1,3-glucanosyltransferase activity have been described in other organisms, such as the Saccharomyces cerevisiae Gas1p or the Aspergillus fumigatus Gel1p. At least four genes encoding putative ?-1,3-glucanosyl-transferases gas1+, gas2+, gas4+ y gas5+- have been identified in the S. pombe sequencing project. In this work, we report the characterization of gas1p, gas2p, gas4p and gas5p during the different stages of the life cycle and their catalytic activity.From the point of view of their functionality, gas1p is essential for cellular viability during vegetative growth, as gas1? null mutants are only able to grow in media supplemented with an osmotic stabilizer. gas4p plays an essential role during the construction of the ascospore wall, being necessary for spore germination. Finally, gas2p and gas5p seem to play a minoritary role in the synthesis of the cell wall, as gas2? and gas5? null mutants or gas2? gas5? double mutant do not show significant morphologic defects.From the biochemical point of view, all of them display ?-1,3-glucanosyl-transferase activity, although they differ in their specificity for the substrate length, the split point and the range of the generated products. Taking all the data into account, together with the differences in their expression profiles during the life cycle, it suggests that the GH72 proteins present in S. pombe may accomplish complementary, non-overlapping, functions in the fission yeast.

[es] La formaci?n de la pared celular de Schizosaccharomyces pombe requiere la actividad coordinada de enzimas involucradas en la bios?ntesis y modificaci?n de sus componentes, entre los que destacan por su abundancia los glucanos. El complejo enzim?tico ?-gluc?n-sintasa sintetiza ?-1,3-glucanos lineales, que permanecen desorganizados y solubles en ?lcali hasta que se establecen enlaces covalentes entre los ?-1,3-glucanos y otros componentes de la pared celular. Las transferasas de la pared celular cuyos sustratos son los ?-1,3-glucanos podr?an estar desempe?ando importantes funciones en el ensamblaje y reordenamiento de la pared celular. Diversas prote?nas pertenecientes a la familia 72 de las glicosil-hidrolasas (GH72) con actividad ?-1,3-glucanosil-transferasa han sido caracterizadas en otros organismos (Gas1p, Gas2p y Gas4p de Saccharomyces cerevisiae, o Gel1p de Aspergillus fumigatus). La secuenciaci?n del genoma de S. pombe ha permitido identificar cuatro genes (gas1+, gas2+, gas4+ y gas5+) que codifican cuatro hipot?ticas prote?nas pertenecientes a la familia GH72.Desde el punto de vista funcional, gas1p es esencial para la viabilidad celular durante el crecimiento vegetativo, ya que los mutantes carentes de este gen s?lo son capaces de crecer en medios estabilizados osm?ticamente. Por su parte, gas4p desempe?a un papel b?sico en la construcci?n de la pared celular de las esporas. Finalmente, las prote?nas gas2p y gas5p deben ejercer un papel minoritario en la s?ntesis de la pared celular vegetativa, ya que mutantes carentes de estos genes (o el doble mutante) no presentan defectos morfol?gicos significativos.Bioqu?micamente, todas ellas poseen actividad ?-1,3-glucanosil-transferasa, aunque se diferencian por la especificidad de longitud de sustrato, el punto de corte y los productos generados. Todo ello, junto con las diferencias de expresi?n a lo largo del ciclo biol?gico, sugiere que las distintas prote?nas de la familia GH72 presentes en S. pombe podr?an estar realizando funciones complementarias, no solapantes, en la levadura de fisi?n.