FIG. 4.

Northern blot analysis of RNA extracted from cells of A. brasilense wild-type and IpdC⁻ mutant strains. (A) Blot of total RNA (10 μg per lane) isolated from A. brasilense IpdC⁻ mutant (lane 1) and wild-type strains (lanes 2 to 5). RNA was visualized by epi-illumination with UV light. Cells were harvested at an OD₆₀₀ of 0.9 (lanes 1 and 3), 0.5 (lane 2), or 0.4 (lanes 4 and 5). To measure the effect of IAA on the transcription of the ipdC gene, the wild-type culture at OD₆₀₀ of 0.4 was divided into two and further incubated for 3 h at 30°C in the absence (lane 4) or presence of exogenously added IAA at 1 mM (lane 5). The positions of the 16S and 23S ribosomal RNAs are indicated at the right. (B) RNA blot analysis of the same samples as in panel A after hybridization with a digoxygenin-labeled ipdC-derived riboprobe. The size of the ipdC transcript (in kilobases) is indicated at the right and was determined relative to RNA standards that were electrophoresed in the same gel.