A, Northern blot analysis of fnbA and saeRS transcription in RN6390 and SH1000 parents and their respective isogenic saeRS mutants after 2, 6, and 12 h incubation in vitro. The blots were hybridized using digoxigenin-labeled polymerase chain reaction (PCR) fragments specific for the indicated transcripts. The different saeRS transcripts (T1, T2, and T3) are specified. Equal loading of RNA samples were confirmed by 23S and 16S ribsomal RNAs. B, Reverse-transcription PCR (RT-PCR) analysis of fnbA expression in RN6390 and SH1000 parents and their respective isogenic saeRS mutants in vitro after 2 h of incubation. C, In vivo fnbA and saeR expression in cardiac vegetations in the infective endocarditis model due to RN6390, SH1000, or their respective saeRS mutants, determined by RT-PCR. Groups 1 and 2 represent fnbA and saeR expression from different animals, respectively; gyrA gene expression was used as an internal control. Lane 1, RN6390; lane 2, ΔsaeRS in RN6390; lane 3, SH1000; lane 4, ΔsaeRS in SH1000.