Transcriptional organization of genes for protocatechuate and quinate degradation from Acinetobacter sp. strain ADP1.

Quinate and protocatechuate are both abundant plant products and can serve, along with a large number of other aromatic or hydroaromatic compounds, as growth substrates for Acinetobacter sp. strain ADP1. The respective genes are part of the chromosomal dca-pca-qui-pob-hca cluster encoding these pathways. The adjacent pca and qui gene clusters, which encode enzymes for protocatechuate breakdown via the beta-ketoadipate pathway and for the conversion of quinate or shikimate to protocatechuate, respectively, have the same direction of transcription and are both expressed inducibly in response to protocatechuate. The pca genes are governed by the transcriptional activator-repressor PcaU. The mechanism governing qui gene expression was previously unknown. Here we report data suggesting the existence of a large 14-kb primary transcript covering the pca and qui genes. The area between the pca and qui genes contains no promoter activity, whereas a weak, constitutive promoter was identified upstream of quiA (quiAp). The 5' end of the quiA transcript was mapped. Northern blot analysis allowed the identification of a 12-kb transcript spanning pcaI to quiX. An analysis of the pca and qui gene transcripts in a strain missing the structural gene promoter pcaIp led to the identification of two pcaIp-independent transcripts (4 and 2.4 kb). The 2.4-kb transcript makes up about 25% of the total transcript abundance of quiA, and thus the majority of transcription of the last gene of the area is also driven by pcaIp. This report strongly supports the organization of the pca and qui genes as a pca-qui operon and, furthermore, suggests that PcaU is the regulator governing its expression.