Figure 1.

Expression of Acr in CSU93 occurs only under reduced oxygen conditions. Two-dimensional gel-electrophoretic analysis of MTB strain CSU93 grown under 20% oxygen (A) and 1.3% oxygen (B). Molecular mass standards for the SDS/PAGE dimension are at the left in kDa and the isoelectric focusing is from basic (left) to acidic (right). Acr is the dominant protein spot in the lower part of the middle of the right gel (arrow). (C) Oxygen-dependent transcription of the acr promoter. A BCG strain transformed with an integrating vector carrying an acr promoter-driven β-gal reporter construct was grown to mid-log phase before splitting the culture and shifting the atmospheric oxygen content to the indicated level. After 6 hr, reporter activity was determined as described in Materials and Methods. In this short interval, no replication occurs and β-gal activity from equivalent numbers of organisms has been plotted.