Modulation of gene expression by (CA)(n) microsatellites in the filamentous ascomycete Podospora anserina

A microsatellite consisting of the alternating pyrimidine-purine sequence ( CA)(n).(TG)(n) is found to occur in very conserved form in the genome of va rious races of the filamentous ascomycete Podospora anserina. Screening of a cDNA library revealed that this sequence is frequently transcribed. In th is study, we focused our attention on a short (CA)(5) microsatellite locate d in the 5' untranslated sequence of the glyceraldehyde-3-phosphate dehydro genase (gpd) gene of P. anserina. Specifically, we investigated whether or not the number of repeat units present in the microsatellite affects the ex pression of the beta-D-glucuronidase (gusA) reporter gene introduced on an autonomously replicating plasmid into fungal protoplasts. The results show that an increase in the number of microsatellite repeat units positively af fects reporter gene expression.