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The polar pili of Pseudomonas aeruginosa are composed of monomers of the pilin structural subunits. The biogenesis of pili involves the synthesis of pilin precursor, cleavage of a six-amino-acid leader peptide, membrane translocation, and assembly of monomers into a filamentous structure extending from the bacterial surface. This report describes three novel genes necessary for the formation of pili. DNA sequences adjacent to piU, the pilin structural gene, were cloned and mutagenized with transposon TnS. Each of the insertions were introduced into the chromosome of P. aeruginosa PAK by gene replacement. The effect of the TnS insertions in the bacterial chromosome on pilus assembly was assessed by electron microscopy and sensitivity of mutants to a pilus-specific bacteriophage. The resultant mutants were also tested for synthesis and membrane localization of the pilin antigen in order to define the genes required for maturation, export, and assembly of pilin. A 4.0-kilobase-pair region of DNA adjacent to the pilin structural gene was found to be essential for formation of pili. This region was sequenced and found to contain three open reading frames coding for 62-, 38-to 45-, and 28-to 32-kilodalton proteins (plB, pilC, and pilD, respectively). Three proteins of similar molecular weight were expressed in Escherichia coli from the 4.0-kilobase-pair fragment flanking piA with use of a T7 promoter-polymerase expression system. The results of the analyses of the three genes and the implications for pilin assembly and maturation are discussed.Pseudomonas aeruginosa is an opportunistic pathogen of humans and is a major cause of morbidity and mortality in patients with cystic fibrosis, certain malignancies, and severe trauma (3). Among the various virulence factors produced by P. aeruginosa, pili have been shown to be important during colonization of mucosal surfaces by mediating the attachment of the bacterium to epithelial cells (6,35).The pilin subunits of P. aeruginosa polar pili resemble those found in a number of other bacterial pathogens in several aspects. Neisseria gonorrhoeae, Moraxella bovis, and Bacteroides nodosus all produce pilins that are similar in primary sequence to those of P. aeruginosa (13,(18)(19)(20). All pilins of this class contain N-methylphenylalanine at the amino terminus and are collectively termed type IV methylphenylalanine pulins. Type IV pilins have another distinguishing characteristic. They are synthesized as prepilins, containing similar N-terminal six-or seven-amino-acid cationic sequences that are absent from the mature pilin subunit. These leader sequences are notably shorter than the typical signal sequences responsible for directing the secretion of many bacterial exported proteins, including membrane translocation of Escherichia coli pilins (1,7,22). The export and assembly of type IV pilins is accompanied by cleavage of the short leader peptide and methylation of the newly formed N-terminal phenylalalanine.We have previously shown that the six-amino-acid leader peptide of the...

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Melanocytic nevi occurring in lymph nodes create diagnostic difficulty by mimicking metastases. Few studies describe nodal nevi in sentinel lymph nodes (SLNs) excised for melanoma. We evaluated 72 cases in which patients had undergone SLN biopsy for melanoma. Lymph nodes and cutaneous melanomas were evaluated according to a standard protocol. Nodal nevi were identified in 8 patients (11%). Of these, 6 (75%) had an associated cutaneous nevus (P = .006). Of 21 patients with an associated nevus, 4 (19%) with nodal nevi had a cutaneous nevus with congenital features (P = .01). The incidence of nodal nevus correlated with a Breslow thickness greater than 2.5 mm (P = .02). Nevi were not seen in non-SLNs. Nodal nevi appear more frequently in patients with melanoma-associated cutaneous nevi, particularly if congenital features are present. The increased frequency of nodal nevi in SLNs relative to non-SLNs suggests an etiology of mechanical transport of nevus cells.

Background The role of systemic chemotherapy (SC) in conjunction with cytoreductive surgery (CS) with hyperthermic intraperitoneal chemotherapy (HIPEC) in appendiceal mucinous carcinoma peritonei (MCP) is unknown. Methods A retrospective review (1999–2011) of MCP patients who had undergone CS/HIPEC with or without perioperative SC. Results Twenty-two low-grade MCP patients treated with CS/HIPEC and SC were matched to patients who received CS/HIPEC alone. Median overall survival (OS) was 107 months for patients treated with perioperative SC compared to 72 without (P = 0.46). CS/HIPEC was performed on 109 patients with high-grade MCP: 70 were treated with perioperative SC, while 39 were not. Median OS (22.1 vs. 19.6 months, P = 0.74) and progression-free survival (PFS) (10.9 vs. 7.0 months, P = 0.47) were similar in patients treated with SC compared to CS/HIPEC alone. Progression while on pre-operative SC was seen in eight patients (17%), while four (8%) had a partial response. Treatment with postoperative SC was associated with longer PFS (13.6 months) compared to pre-operative SC (6.8 months, P < 0.01) and CS/HIPEC alone (7.0 months, P = 0.03). Conclusions Post-operative SC appears to improve PFS in patients with high-grade appendiceal MCP treated with CS/HIPEC. In contrast, there is no evidence to support the routine use of perioperative SC in low-grade disease.