Kinetics of toxA and regA mRNA accumulation in Pseudomonas aeruginosa

DNA probes specific for an internal portion of the toxA and regA genes were used to examine the synthesis of mRNA during the growth cycle of P. aeruginosa PA103. RNA dot blot analysis revealed that in a low-iron growth medium, the synthesis of regA and toxA mRNA followed a biphasic expression pattern. Analysis of ADP-ribosyltransferase activity also indicated that an early and late phase of exotoxin A synthesis occurred. Utilizing an internal SalI probe, examination of the size distribution of the regA mRNA during the cell cycle indicated that a large transcript (T1) was present at early time points, followed by the appearance of a smaller transcript (T2) during late exponential to early stationary phase. An upstream AvaI regA probe was found to hybridize to the T1 transcript but not to the T2 transcript. The data indicate that at least two separate functional regA mRNA species were produced. Analysis of mRNA accumulation for the regA gene when cells were grown in high-iron medium provided additional evidence for two separately controlled transcripts being produced from the regA chromosomal locus. Both regA transcripts were correlated with exotoxin A transcription and production.