Growth characteristics of the secDF mutant. (A) Genetic context of secDF in S. aureus and Northern blot analysis of secDF transcription during growth. Predicted promoter and terminators are depicted. Ethidium bromide-stained 16S rRNA is shown as an indication of RNA loading. (B) Growth of Newman and the secDF mutant carrying the empty vector pCN34, and of the complemented mutant secDF pCQ27 in LB broth at 37°C and 15°C, respectively.