Fig. 5.

HlyU regulates both hemolysin clusters positively at the transcriptional level. Semiquantitative RT-PCR was used to determine the expression levels of rtxA, rtxB, rtxH, vah1, and plp with 100 μg of RNA extracted from V. anguillarum cells grown to the exponential phase (A) and stationary phase (B). Data show that the expression of rtxA, rtxB, and rtxH decreased in the hlyU mutant (S305). However, expression of vah1 and plp did not decrease in S305, but did increase in the hlyU complement (S307). The M93Sm genomic DNA was used as a positive control (+). RT-PCRs with no added reverse transcriptase used as negative controls showed no amplified bands (data not shown). The DNA molecular size standards (Std) are a 100-bp Promega DNA ladder.