Transcription of the fimbrial subunit gene and an associated transfer RNA gene of Pseudomonas aeruginosa.

Gene fimA encoding the structural subunit of the fimbriae of Pseudomonas aeruginosa PAK is located in the centre of a 1.2-kb HindIII genomic DNA fragment [see also Sastry et al., J. Bacteriol. 164 (1985) 571-577], which in turn is located within a 6.2-kb EcoRI fragment. Immediately downstream from fimA is a putative threonine tRNA gene [Dalrymple and Mattick, Biochem. Int. 13 (1986) 547-553]. Northern blotting experiments showed that fimA is transcribed to an mRNA of approx. 650 nucleotides, which also includes the threonine tRNA sequence but no other protein-coding region. There was no indication that this mRNA is processed to release the tRNA sequence. However, the tRNA did appear to be expressed independently from its own promoter in the region 3' to fimA. When these sequences were introduced into Pseudomonas putida, we found that the level of expression of fimA from the cloned 6.2-kb EcoRI fragment was approx. 30-fold greater than that from the smaller HindIII fragment, whereas that of the specific tRNA species was unaltered. The size of the fimA transcript was also unaltered. These results provide evidence that the fimA gene is subject to specific transcriptional activation in vivo and that this activation involves sequences flanking the 1.2-kb HindIII fragment.