The ileS-lsp operon in Escherichia coli is located at 0.5 min on the E. coli genetic map (17). The operon consists of ileS, the structural gene for isoleucyl-tRNA synthetase; Isp, the gene that encodes prolipoprotein signal peptidase (4, 26); and three open reading frames designated x (8), orf949, and or9316 (11). Gene x encodes a soluble protein with an apparent Mr of 35,000. The gene products of or9749 and or9316 have not been identified. Signal peptidase II (SPase II), an inner membrane enzyme, cleaves lipid-modified prolipoprotein to form apolipoprotein, which is further modified by N-acylation to yield mature Braun's lipoprotein (22). Although there is no apparent physiological connection between the activation of isoleucine by isoleucyl-tRNA synthetase and the proteolytic cleavage of lipid-modified prolipoprotein by SPase II, these two genes are cotranscribed with the three open reading frames in the operon. In a previous paper, we showed that all five of these genes present in the E. coli ileS-lsp operon were also found in Enterobacter aerogenes in the same order as in E. coli (6).Braun's lipoprotein and homologous lipoproteins appear throughout the gram-negative bacteria (reviewed in reference 24). In a study by Nakamura et al. (16), antisera raised against E. coli Braun's lipoprotein cross-reacted with homologous lipoproteins in all members of the family Enterobacteriaceae tested, but no cross-reactivity was observed with Pseudomonas aeruginosa and with three other nonenteric bacteria. These results indicated that the homolog of Braun's lipoprotein in P. aeruginosa, lipoprotein I (14), is antigenically unrelated to those in enteric bacteria. Although glyceride-modified cysteine has not been unequivocally demonstrated in P. aeruginosa lipoprotein, glycerol and fatty acid incorporations into lipoprotein I (14) and lipoprotein H, a peptidoglycan-associated lipoprotein (13), have been detected. A recent study by Duchene et al. (2) has shown that in lipoprotein I, the amino acid sequence at the SPase II cleavage site is Leu-Ala-Thr-Gly-Cys-Ser-Ser, which is very

In Escherichia coli, prolipoprotein signal peptidase is encoded by the Isp gene, which is organized into an operon consisting of ileS, Isp, and three open reading frames, designated genes x, orf-149, and orf-316. The Enterobacter aerogenes Isp gene was cloned and expressed in E. coli. The nucleotide sequence of the Enterobacter aerogenes Isp gene and a part of its flanking sequences were determined. A high degree of homology was found between the E. coli ileS-isp operon and the corresponding genes in Enterobacter aerogenes. Furthermore, the same five genes which constitute an operon in E. coli were found in Enterobacter aerogenes in the same order.

A 480 transducing phage, 480immXdhis, carrying the Salmonella his-gnd region, was characterized by immunity studies, tonB deletion analysis, and marker rescue analysis. 480immXdhis retains the phage immunity region ofthe +80-X hybrid phage from which it was derived. Bacterial genes replace most late phage genes. Deletion analysis shows the prophage gene order to be immX-hisgnd and indicates the orientation of the his operon to be hisOGDCBHAFIEgnd. The structure of 480immXdhis is remarkably similar to two independently isolated 0480 phages that carry the his-gnd region of Escherichia coli and that, like q580immXdhis, were derived by directed gene transposition to the tonB locus. A derivative of 480immXdhis that is 480 immune is also reported.