Clustered genes with a higher transcript level in the DS50661. Transcript levels of a cluster of genes of which many exclusively had higher transcript levels in the cluster-free strain DS50661 than in the penicillin-high-producing strain DS17690 irrespective of the side chain precursor. Annotation of many of these genes and their clustering suggests a role in secondary metabolite production. Total RNA was obtained from P. chrysogenum strains DS17690 and DS50661, grown in the presence and absence of phenylacetic acid (PAA) in independent glucose-chemostat cultures at D = 0.03 h-1 and hybridized to Affymetrix GeneChip® microarrays. *, genes with a significantly higher transcript level (fold change > 2, FDR 1%) in DS50661 compared to DS17690.