GLUCOSE-INDUCED SECRETION OF TRICHODERMA-REESEI XYLANASES

To produce two xylanases with Trichoderma reesei grown on glucose, rec ombinant strains which carry either the xyn1 or the xyn2 (xylanase I a nd II [XYN I and XYN II]-encoding) structural genes under the expressi on signals of the homologous pki1 (pyruvate kinase-encoding) gene were constructed. The two types of transformants secreted XYN I or II, res pectively, during growth on glucose, as demonstrated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunostaining, The co rresponding specific xylanase activities of the best transformants on glucose were 76 and 145 U/mg of protein for XYN I and XYN II, respecti vely, as opposed to that obtained by the parent strain (26 U/mg of pro tein), When related to the amount of biomass formed, however, they pro duced only about 4 to 5 U/g, in contrast to much higher activities (10 to 12 U/g) during growth on xylan, The ultrastructural location of XY N II in the transformant strain producing the highest constitutive XYN II formation (ATX2-12) was investigated by immunoelectron microscopy and compared with that in the wild-type strain growing on xylan, Cell extracts from both types of transformants grown on glucose exhibited a higher intracellular xylanase activity than did the parent strain gro wn on xylan, By using electron microscopy and immunogold labelling, XY N II was detected in the endoplasmic reticulum, Golgi-like vesicles, s ecretory vesicles, vacuoles, and cell walls, The immunolabel in the va cuoles was detected preferentially in subapical cells, When a recombin ant strain which expressed xyn2 from the pki1 promoter was compared wi th the parent strain during growth on xylan, the former exhibited a le ss proliferated endoplasmic reticulum and a smaller number of secretor y vesicles; however, a higher density of labelling was observed. The r elationship of these findings to the efficacy of protein secretion dur ing growth on glucose is discussed.