lep operon proximal gene is not required for growth or secretion by Escherichia coli

Leader peptidase is an essential enzyme of Escherichia coli and is required for protein export. The structural gene for leader peptidase (lep) is separated from its promoter by an upstream gene of unknown function (lepA). The gene lepA was shown by the use of minicell analysis and overproduction to encode a protein of 74,000 daltons. To determine whether this 74,000-dalton protein functions in protein export, a mutant of E. coli H560 was constructed which has a 1.5-kilobase-pair deletion in the lepA gene. The lepA deletion mutant had no apparent defect for growth or protein export, indicating that lepA is nonessential and that the two cotranscribed genes lepA and lep probably have unrelated functions.