March P E, Inouye M
J Biol Chem. 1985 Jun 25;260(12):7206-13.
The DNA sequence flanking the gene (lep) encoding signal peptidase I of Escherichia coli has been determined. The upstream flanking sequence contains a gene (lepA) that encodes a polypeptide of 598 amino acid residues and terminates 18 base pairs from the initiation codon of the lep gene. The position of the lep promoter was determined by both gene fusion with the lacZ gene as well as by S1 nuclease mapping of the lep mRNA to be 73 base pairs upstream from the initiation codon of the lepA gene. The lepA gene was cloned into a high expression vector (pIN-III), and its gene product was identified to be a protein of apparent molecular weight of 76,000. This gene product was preferentially localized in the cytoplasmic membrane and periplasmic fractions upon subcellular fractionation. The DNA sequence immediately downstream of the lep gene contains features consistent with a rho factor-independent transcriptional termination site, indicating that the lep operon encodes only two proteins (lepA and lep).
已确定了大肠杆菌中编码信号肽酶I的基因（lep）两侧的DNA序列。上游侧翼序列包含一个基因（lepA），该基因编码一个由598个氨基酸残基组成的多肽，并在距离lep基因起始密码子18个碱基对处终止。通过与lacZ基因的基因融合以及对lep mRNA的S1核酸酶作图，确定lep启动子位于lepA基因起始密码子上游73个碱基对处。将lepA基因克隆到一个高表达载体（pIN-III）中，其基因产物被鉴定为一种表观分子量为76,000的蛋白质。在亚细胞分级分离后，该基因产物优先定位于细胞质膜和周质部分。lep基因紧下游的DNA序列包含与rho因子非依赖性转录终止位点一致的特征，表明lep操纵子仅编码两种蛋白质（lepA和lep）。
