CATABOLITE REPRESSION OF INDUCTIVE POLYGALACTURONASE SYNTHESIS IN PENICILLIUM-EXPANSUM BY SUCROSE

Polygalacturonase (PG) synthesis by the fungus Penicillium expansum in the presence of a combination of pectin and sucrose corresponding to 0.3 % of the substrate was repressed more intensely by increasing sucr ose concentrations and decreasing pectin concentrations. PG synthesis was partially repressed when sucrose was added 6 or 12 h after the beg inning of culture and fully repressed when sucrose was added at the be ginning of culture. Tests with actidione indicated that repression by sucrose occurs at the transcription level. We suggest that an accumula tion of messenger RNA occurred when the fungus was cultured for 36 h i n 0.3 % pectin and actidione since, after being washed and reincubated in actidione-free medium in the presence of the repressor, the fungus synthesized PG up to 54 h of culture, when a reduction in accumulated messenger RNA and PG synthesis occurred. Repression by sucrose was re versible since the fungus started synthesizing PG again in the absence of the repressor and in the presence of the inducer.