FIG 8.

Model showing that the expression of Sle1 is coupled to the TP activity of PBPs. The model predicts that the TP activity of PBPs plays a role in signaling that peptidoglycan synthesis is complete and that it is time to activate the expression of Sle1. In the absence of β-lactam antibiotics, the TP activity of both native PBPs and the mecA-encoded PBP2a contribute to the cross-linking of peptidoglycan and to the activation of Sle1 expression. In cells exposed to β-lactam antibiotics, however, the TP activity of native PBPs is inhibited by the irreversible binding of oxacillin, and the expression of Sle1 becomes entirely dependent on the TP activity of PBP2a. PBP2a is less efficient in promoting expression of Sle1 than are the native PBPs, and therefore the Sle1 levels are reduced in JE2 cells exposed to oxacillin. See the text for details.