Elevated cytosolic concentrations of SecA compensate for a protein translocation defect in Escherichia coli cells with reduced levels of negatively charged phospholipids.

Cellular extracts from cells with reduced synthesis of negatively charged phospholipids were found to support in vitro translocation of the precursor of the outer membrane protein PhoE with increased efficiency. Analysis of these extracts revealed that they contain increased levels of SecA. SecA depletion resulted in a loss of the translocation stimulatory activity, which could be restored by re-addition of purified SecA. We conclude that elevated cytosolic levels of SecA counteract the reduction of translocation efficiency due to low levels of negatively charged phospholipids in the inner membrane.