Nucleotide sequence of the traD region in the Escherichia coli F sex factor

Comparative genome analysis of three classical E. coli cloning strains designed for blue/white selection: JM83, JM109 and XL1-Blue

The development of the Escherichia coli K-12 laboratory strains JM83, JM109 and XL1-Blue was instrumental in early gene technology. We report the comprehensive genome sequence analysis of JM83 and XL1-Blue using Illumina and Oxford Nanopore technologies and a comparison with both the wild-type sequence (MG1655) and the genome of JM109 deposited at GenBank. Our investigation provides insight into the way how the genomic background that allows blue/white colony selection-by complementing a functionally inactive ω-fragment of β-galactosidase (LacZ) with its α-peptide encoded on the cloning vector-has been implemented independently in these three strains using classical bacterial genetics. In fact, their comparative analysis reveals recurrent motifs: (i) inactivation of the native enzyme via large deletions of chromosomal regions encompassing the lac locus, or a chemically induced frameshift deletion at the beginning of the lacZ cistron, and (ii) utilization of a defective prophage (ϕ80), or an F'-plasmid, to provide the lacZ∆M15 allele encoding its ω-fragment. While the genetic manipulations of the E. coli strains involved repeated use of mobile genetic elements as well as harsh chemical or physical mutagenesis, the individual modified traits appear remarkably stable as they can be found even in distantly related laboratory strains, beyond those investigated here. Our detailed characterization at the genome sequence level not only offers clues about the mechanisms of classical gene transduction and transposition but should also guide the future fine-tuning of E. coli strains for gene cloning and protein expression, including phage display techniques, utilizing advanced tools for site-specific genome engineering.

Benchmark of site- and structure-specific quantitative tissue N-glycoproteomics for discovery of potential N-glycoprotein markers: a case study of pancreatic cancer

Pancreatic cancer is a highly malignant tumor of the digestive tract that is difficult to diagnose and treat. It is more common in developed countries and has become one of the main causes of death in some countries and regions. Currently, pancreatic cancer generally has a poor prognosis, partly due to the lack of symptoms in the early stages of pancreatic cancer. Therefore, most cases are diagnosed at advanced stage. With the continuous in-depth research of glycoproteomics in precision medical diagnosis, there have been some reports on quantitative analysis of cancer-related cells, plasma or tissues to find specific biomarkers for targeted therapy. This research is based on the developed complete N-linked glycopeptide database search engine GPSeeker, combined with liquid-mass spectrometry and stable diethyl isotope labeling, providing a benchmark of site- and structure-specific quantitative tissue N-glycoproteomics for discovery of potential N-glycoprotein markers. With spectrum-level FDR ≤1%, 20,038 intact N-Glycopeptides corresponding to 4518 peptide backbones, 228 N-glycan monosaccharide compositions 1026 N-glycan putative structures, 4460 N-glycosites and 3437 intact N-glycoproteins were identified. With the criteria of ≥1.5-fold change and p value<0.05, 52 differentially expressed intact N-glycopeptides (DEGPs) were found in pancreatic cancer tussues relative to control, where 38 up-regulated and 14 down-regulated, respectively.

Translational readthrough generates new astrocyte AQP4 isoforms that modulate supramolecular clustering, glial endfeet localization, and water transport

Regulation of water homeostasis is a central feature of central nervous system pathophysiology. In this context, several lines of evidence suggest a crucial role for the water channel aquaporin-4 (AQP4) and its plasma membrane supramolecular organization as the key element. Here, we demonstrate the expression in tissues of additional isoforms of AQP4 characterized by a C-terminal extension generated by programmed translational readthrough. These extended isoforms (AQP4ex) display a perivascular polarization and expression in dystrophin-dependent pools. AQP4ex reduces supramolecular clustering tendency and allows AQP4 interactions with syntrophin. Furthermore, site-directed mutagenesis of two serines in the extended C-terminus of AQP4ex showed potential regulation of water permeability by phosphorylation. Finally, AQP4ex expression can be positively modulated by gentamicin treatment, demonstrating the possibility of regulating the AQP4 translational readthrough frequency. This novel regulatory mechanism could have important pathophysiological implications for conditions in which alternations have been reported in AQP4 structure.

Plasmid r1 conjugative DNA processing is regulated at the coupling protein interface

Selective substrate uptake controls initiation of macromolecular secretion by type IV secretion systems in gram-negative bacteria. Type IV coupling proteins (T4CPs) are essential, but the molecular mechanisms governing substrate entry to the translocation pathway remain obscure. We report a biochemical approach to reconstitute a regulatory interface between the plasmid R1 T4CP and the nucleoprotein relaxosome dedicated to the initiation stage of plasmid DNA processing and substrate presentation. The predicted cytosolic domain of T4CP TraD was purified in a predominantly monomeric form, and potential regulatory effects of this protein on catalytic activities exhibited by the relaxosome during transfer initiation were analyzed in vitro. TraDDeltaN130 stimulated the TraI DNA transesterase activity apparently via interactions on both the protein and the DNA levels. TraM, a protein interaction partner of TraD, also increased DNA transesterase activity in vitro. The mechanism may involve altered DNA conformation as TraM induced underwinding of oriT plasmid DNA in vivo (DeltaL(k) = -4). Permanganate mapping of the positions of duplex melting due to relaxosome assembly with TraDDeltaN130 on supercoiled DNA in vitro confirmed localized unwinding at nic but ruled out formation of an open complex compatible with initiation of the TraI helicase activity. These data link relaxosome regulation to the T4CP and support the model that a committed step in the initiation of DNA export requires activation of TraI helicase loading or catalysis.

Analysis and characterization of the IncFV plasmid pED208 transfer region

pED208 is a transfer-derepressed mutant of the IncFV plasmid, F(0)lac, which has an IS2 element inserted in its traY gene, resulting in constitutive overexpression of its transfer (tra) region. The pED208 transfer region, which encodes proteins responsible for pilus synthesis and conjugative plasmid transfer, was sequenced and found to be very similar to the F tra region in terms of its organization although most pED208 tra proteins share only about 45% amino acid identity. All the essential genes for F transfer had homologs within the pED208 transfer region with the exception of traQ, which encodes the chaperone for stable F-pilin expression. F(0)lac appears to have a fertility inhibition system different than the FinOP system of other F-like plasmids, and its transfer efficiency was increased in the presence of F or R100, suggesting that it could be mobilized by these plasmids. The F-like transfer systems specified by F, R100, and F(0)lac were highly specific for their cognate origins of transfer (oriT) as measured by their abilities to mobilize chimeric oriT-containing plasmids.

Molecular evolution of the pathogenicity island of enterotoxigenic Bacteroides fragilis strains

Enterotoxigenic Bacteroides fragilis (ETBF) strains, which produce a 20-kDa zinc metalloprotease toxin (BFT), have been associated with diarrheal disease in animals and young children. Studying a collection of ETBF and nontoxigenic B. fragilis (NTBF) strains, we found that bft and a second metalloprotease gene (mpII) are contained in an approximately 6-kb pathogenicity island (termed B. fragilis pathogenicity island or BfPAI) which is present exclusively in all 113 ETBF strains tested (pattern I). Of 191 NTBF strains, 100 (52%) lack both the BfPAI and at least a 12-kb region flanking BfPAI (pattern II), and 82 of 191 NTBF strains (43%) lack the BfPAI but contain the flanking region (pattern III). The nucleotide sequence flanking the left end of the BfPAI revealed a region with the same organization as the mobilization region of the 5-nitroimidazole resistance plasmid pIP417 and the clindamycin resistance plasmid pBFTM10, that is, two mobilization genes (bfmA and bfmB) organized in one operon and a putative origin of transfer (oriT) located in a small, compact region. The region flanking the right end of the BfPAI contains a gene (bfmC) whose predicted protein shares significant identity to the TraD mobilization proteins encoded by plasmids F and R100 from Escherichia coli. Nucleotide sequence analysis of one NTBF pattern III strain (strain I-1345) revealed that bfmB and bfmC are adjacent to each other and separated by a 16-bp GC-rich sequence. Comparison of this sequence with the appropriate sequence of ETBF strain 86-5443-2-2 showed that in this ETBF strain the 16-bp sequence is replaced by the BfPAI. This result defined the BfPAI as being 6,036 bp in length and its precise integration site as being between the bfmB and bfmC stop codons. The G+C content of the BfPAI (35%) and the flanking DNA (47 to 50%) differ greatly from that reported for the B. fragilis chromosome (42%), suggesting that the BfPAI and its flanking region are two distinct genetic elements originating from very different organisms. ETBF strains may have evolved by horizontal transfer of these two genetic elements into a pattern II NTBF strain.

Comparison of proteins involved in pilus synthesis and mating pair stabilization from the related plasmids F and R100-1: insights into the mechanism of conjugation

F and R100-1 are closely related, derepressed, conjugative plasmids from the IncFI and IncFII incompatibility groups, respectively. Heteroduplex mapping and genetic analyses have revealed that the transfer regions are extremely similar between the two plasmids. Plasmid specificity can occur at the level of relaxosome formation, regulation, and surface exclusion between the two transfer systems. There are also differences in pilus serology, pilus-specific phage sensitivity, and requirements for OmpA and lipopolysaccharide components in the recipient cell. These phenotypic differences were exploited in this study to yield new information about the mechanism of pilus synthesis, mating pair stabilization, and surface and/or entry exclusion, which are collectively involved in mating pair formation (Mpf). The sequence of the remainder of the transfer region of R100-1 (trbA to traS) has been completed, and the complete sequence is compared to that of F. The differences between the two transfer regions include insertions and deletions, gene duplications, and mosaicism within genes, although the genes essential for Mpf are conserved in both plasmids. F+ cells carrying defined mutations in each of the Mpf genes were complemented with the homologous genes from R100-1. Our results indicate that the specificity in recipient cell recognition and entry exclusion are mediated by TraN and TraG, respectively, and not by the pilus.

Identification of a cytolethal distending toxin gene locus and features of a virulence-associated region in Actinobacillus actinomycetemcomitans

A genetic locus for a cytolethal distending toxin (CDT) was identified in a polymorphic region of the chromosome of Actinobacillus actinomycetemcomitans, a predominant oral pathogen. The locus was comprised of three open reading frames (ORFs) that had significant amino acid sequence similarity and more than 90% sequence identity to the cdtABC genes of some pathogenic Escherichia coli strains and Haemophilus ducreyi, respectively. Sonic extracts from recombinant E. coli, containing the A. actinomycetemcomitans ORFs, caused the distension and killing of Chinese hamster ovary cells characteristic of a CDT. Monoclonal antibodies made reactive with the CdtA, CdtB, and CdtC proteins of H. ducreyi recognized the corresponding gene products from the recombinant strain. CDT-like activities were no longer expressed by the recombinant strain when an OmegaKan-2 interposon was inserted into the cdtA and cdtB genes. Expression of the CDT-like activities in A. actinomycetemcomitans was strain specific. Naturally occurring expression-negative strains had large deletions within the region of the cdt locus. The cdtABC genes were flanked by an ORF (virulence plasmid protein), a partial ORF (integrase), and DNA sequences (bacteriophage integration site) characteristic of virulence-associated regions. These results provide evidence for a functional CDT in a human oral pathogen.

The carboxyl terminus of protein TraD adds specificity and efficiency to F-plasmid conjugative transfer

We isolated and characterized traD mutants with an altered specificity of interaction with relaxosomes of various conjugative (F and R388) and mobilizable (RSF1010 and ColE1) plasmids. The change in specificity was due to a loss of some amino acids in the carboxyl terminus of TraD that resulted in a broadening of the range of mobilizable relaxosomes at the expense of a decrease in the efficiency of F-plasmid transfer.

The cytoplasmic DNA-binding protein TraM binds to the inner membrane protein TraD in vitro

The cytoplasmic protein TraM is one of four essential gene products of the F factor which are involved in DNA transfer after mating pair formation. TraM binds to three specific sites within the oriT region. Besides regulation of its own synthesis, the precise function of TraM during conjugation is not yet known. In the present work, the affinity of TraM to TraD was studied in vitro by an overlay assay and by affinity chromatography. Whether the interaction between TraM and TraD causes a transient or permanent anchoring of the F factor to the site of transfer is discussed. A 35-kDa host membrane protein of yet unknown function also shows affinity to TraM and may be involved in this anchoring process as well.

Plasmid maintenance functions of the large virulence plasmid of Shigella flexneri

The large virulence plasmid pMYSH6000 of Shigella flexneri contains a replicon and a plasmid maintenance stability determinant (Stb) on adjacent SalI fragments. The presence of a RepFIIA replicon on the SalI C fragment was confirmed, and the complete sequence of the adjacent SalI O fragment was determined. It shows homology to part of the transfer (tra) operon of the F plasmid. Stb stabilizes a partition-defective P1 miniplasmid in Escherichia coli. A 1.1-kb region containing a homolog of the F trbH gene was sufficient to confer stability. However, the trbH open reading frame could be interrupted without impairing stability. Deletion analysis implicated the involvement of two small open reading frames, STBORF1 and STBORF2, that fully overlap trbH in the opposite direction. These open reading frames are closely related to the vagC and vagD genes of the Salmonella dublin virulence plasmid and to open reading frame pairs in the F trbH region and in the chromosomes of Dichelobacter nodosus and Haemophilus influenzae. Stb appears to promote better-than-random distribution of plasmid copies and is a plasmid incompatibility determinant. The F homolog does not itself confer stability but exerts incompatibility against the activity of the Stb system. Stb is likely to encode either an active partition system or a postsegregational killing system. It shows little similarity to previously studied plasmid stability loci, but the genetic organization of STBORF1 and STBORF2 resembles that of postsegregational killing mechanisms.

Essential motifs of relaxase (TraI) and TraG proteins involved in conjugative transfer of plasmid RP4

Two essential transfer genes of the conjugative plasmid RP4 were altered by site-directed mutagenesis: traG of the primase operon and traI of the relaxase operon. To evaluate effects on the transfer phenotype of the point mutations, we have reconstituted the RP4 transfer system by fusion of the transfer regions Tra1 and Tra2 to the small multicopy replicon ColD. Deletions in traG or traI served to determine the Tra phenotype of mutant plasmids by trans complementation. Two motifs of TraG which are highly conserved among TraG-like proteins in several other conjugative DNA transfer systems were found to be essential for TraG function. One of the motifs resembles that of a nucleotide binding fold of type B. The relaxase (TraI) catalyzes the specific cleaving-joining reaction at the transfer origin needed to initiate and terminate conjugative DNA transfer (W. Pansegrau, W. Schröder, and E. Lanka, Proc. Natl. Acad. Sci. USA 90:2925-2929, 1993). Phenotypes of mutations in three motifs that belong to the active center of the relaxase confirmed previously obtained biochemical evidence for the contributions of the motifs to the catalytic activity of TraI. Expression of the relaxase operon is greatly increased in the absence of an intact TraI protein. This finding suggests that the relaxosome which assembles only in the presence of the TraI in addition to its enzymatic activity plays a role in gene regulation.

Analysis of the sequence and gene products of the transfer region of the F sex factor

Bacterial conjugation results in the transfer of DNA of either plasmid or chromosomal origin between microorganisms. Transfer begins at a defined point in the DNA sequence, usually called the origin of transfer (oriT). The capacity of conjugative DNA transfer is a property of self-transmissible plasmids and conjugative transposons, which will mobilize other plasmids and DNA sequences that include a compatible oriT locus. This review will concentrate on the genes required for bacterial conjugation that are encoded within the transfer region (or regions) of conjugative plasmids. One of the best-defined conjugation systems is that of the F plasmid, which has been the paradigm for conjugation systems since it was discovered nearly 50 years ago. The F transfer region (over 33 kb) contains about 40 genes, arranged contiguously. These are involved in the synthesis of pili, extracellular filaments which establish contact between donor and recipient cells; mating-pair stabilization; prevention of mating between similar donor cells in a process termed surface exclusions; DNA nicking and transfer during conjugation; and the regulation of expression of these functions. This review is a compendium of the products and other features found in the F transfer region as well as a discussion of their role in conjugation. While the genetics of F transfer have been described extensively, the mechanism of conjugation has proved elusive, in large part because of the low levels of expression of the pilus and the numerous envelope components essential for F plasmid transfer. The advent of molecular genetic techniques has, however, resulted in considerable recent progress. This summary of the known properties of the F transfer region is provided in the hope that it will form a useful basis for future comparison with other conjugation systems.

Analysis of a transfer region from the staphylococcal conjugative plasmid pSK41

The nucleotide sequence of a 14.4-kb region (tra) associated with DNA transfer of the staphylococcal conjugative plasmid, pSK41, has been determined. Analysis of the sequence revealed the presence of 15 genes potentially involved in the conjugative process. Polypeptide products likely to correspond to ten of these genes have been identified, of which one was found to be a lipoprotein. Comparison of the deduced tra products to the protein databases revealed several interesting similarities, one of which suggests an evolutionary link between this Gram+ bacterial conjugation system and DNA transfer systems of Gram- bacteria, such as Escherichia coli and Agrobacterium tumefaciens. The nt sequence also provided an insight into the transcriptional organisation and regulation of the region.

The virD4 gene is required for virulence while virD3 and orf5 are not required for virulence of Agrobacterium tumefaciens

The virD operon of the resident Ti plasmid of Agrobacterium tumefaciens contains loci involved in T-DNA processing and undefined virulence functions. Nucleotide sequence of the entire virD operon of pTiC58 revealed similarities to the virD operon of the root-inducing plasmid pRiA4b and to that of the octopine-type plasmid pTiA6NC. However, comparative sequence data show that virD of pTiC58 is more akin to that of the pRiA4b than to that of the pTiA6NC. T7f10::virD gene fusions were used to generate polypeptides that confirm the presence of four open reading frames virD1, virD2, virD3, and virD4 within virD which have a coding capacity for proteins of 16.1, 49.5, 72.6, and 73.5 kDa, respectively. virD3 therefore encodes a polypeptide 3.4 times larger (72.6 versus 21.3 kDa) than that encoded by virD3 of octopine Ti plasmids. Non-polar virD4 mutants could not be complemented by a distant homologue, TraG protein of plasmid RP4. An independently regulated fifth ORF (orf5) is located immediately downstream of 3' end of virD4 and encodes a polypeptide of 97.4 kDa. The expression of orf5 is dependent on its own promoter and is independent of acetosyringone induction in A. tumefaciens. Recently, it has been shown that virD3 of octopine Ri or Ti plasmids is not required for virulence. In this report, we confirm and extend these findings on a nopaline Ti plasmid by using several virD non-polar mutants that were tested for virulence. virD3 and orf5 non-polar mutants showed no effect on tumorigenicity on 14 different plant species, while virD4 mutants lost their tumorigenicity completely on all these test plants. These data suggest that virD3 and orf5 are not essential for virulence whereas virD4 is absolutely required on a wide range of host plants.

Subcellular localization of seven VirB proteins of Agrobacterium tumefaciens: implications for the formation of a T-DNA transport structure

Plant cell transformation by Agrobacterium tumefaciens involves the transfer of a single-stranded DNA-protein complex (T-complex) from the bacterium to the plant cell. One of the least understood and important aspects of this process is how the T-complex exits the bacterium. The eleven virB gene products have been proposed to specify the DNA export channel on the basis of their predicted hydrophobicity. To determine the cellular localization of the VirB proteins, two different cell fractionation methods were employed to separate inner and outer membranes. Seven VirB-specific antibodies were used on Western blots (immunoblots) to detect the proteins in the inner and outer membranes and soluble (containing cytoplasm and periplasm) fractions. VirB5 was in both the inner membrane and cytoplasm. Six of the VirB proteins were detected in the membrane fractions only. Three of these, VirB8, VirB9, and VirB10, were present in both inner and outer membrane fractions regardless of the fractionation method used. Three additional VirB proteins, VirB1, VirB4, and VirB11, were found mainly in the inner membrane fraction by one method and were found in both inner and outer membrane fractions by a second method. These results confirm the membrane localization of seven VirB proteins and strengthen the hypothesis that VirB proteins are involved in the formation of a T-DNA export channel or gate. That most of the VirB proteins analyzed are found in both inner and outer membrane fractions suggest that they form a complex pore structure that spans both membranes, and their relative amounts in the two membrane fractions reflect their differential sensitivity to the experimental conditions.

Molecular characterization of a genomic region associated with virulence in Dichelobacter nodosus

The major pathogen implicated in footrot, a highly contagious disease of sheep, is the strict anaerobe Dichelobacter nodosus (formerly Bacteroides nodosus). Sequence analysis of a 2,262-bp segment of the D. nodosus genome which is more prevalent in virulent isolates than in other isolates showed the presence of four open reading frames which appeared to have consensus transcriptional and translational start signals. These virulence-associated genes have been designated vapABCD. Two of the three copies of the vap region in the genome of the reference strain D. nodosus A198 were shown to carry all of the vap genes, whereas one copy contained only the vapD gene. The VapD protein was gel purified, shown to contain the predicted amino-terminal sequence, and used to raise rabbit antibodies. Western blots (immunoblots) showed that all of the D. nodosus strains tested that contained the vap region produced the VapD protein. The VapD protein had significant amino acid sequence identity with open reading frame 5 from the cryptic plasmid of Neisseria gonorrhoeae, and the vapBC operon had sequence similarity with the trbH region of the Escherichia coli F plasmid. It is proposed that these gene regions evolved from the integration of a conjugative plasmid from another bacterial species into the D. nodosus chromosome.

Characterization of the F plasmid bifunctional conjugation gene, traG

The Escherichia coli F plasmid gene, traG, is required for two stages of the conjugation process: pilus biosynthesis and mating aggregate stabilization. The nucleotide sequence of traG has been determined and the topology of its product in the cytoplasmic membrane analysed using protease accessibility experiments. Complementation analysis employing plasmid deletions revealed a correlation between an N-terminal periplasmic segment of the protein product (TraGp) and its pilus assembly activity. Production of an anti-TraGp antiserum has facilitated the detection of TraGp*, a possible internal cleavage product of TraGp. Although its function is unknown. TraGp* is located in the periplasm and has been shown to possess sequences required for aggregate stabilization. The detection of TraGp* raises the possibility that the two functions of traG are carried out by separate products.

Construction and characterization of derivatives carrying insertion mutations in F plasmid transfer region genes, trbA, artA, traQ, and trbB

We devised a method for construction of insertion mutations in F plasmid tra region genes as a means of investigating the functions associated with previously uncharacterized loci. First, we constructed mutations in vitro, by insertion of a kanamycin resistance gene into a unique restriction site within a tra region fragment carried by a small, chimeric plasmid. Second, we crossed the insertion mutations, in vivo, onto a plasmid containing the complete F tra region sequence (either F lac, or pOX38, a Tra+ F plasmid derivative). Using this method, we obtained F lac mutant derivatives carrying KmR gene insertions in traQ, and a set of pOX38 mutant derivatives carrying a KmR gene insertion in trbA, artA, traQ, or trbB. Analysis of these derivatives showed that insertion of a kan gene at the NsiI site of traQ resulted in transfer deficiency, F-pilus-specific-phage resistance and an absence of detectable F-pilin subunit synthesis. Since the traQ mutants regained a wild-type phenotype when complemented with a traQ+ plasmid clone, we concluded that traQ expression is essential to transfer and F-pilus synthesis. However, pOX38 derivatives carrying kan gene inserts in genes trbA, artA, or trbB retained F-pilus-specific phage sensitivity and transferred at normal levels. Thus, these three gene products may not be essential for F-transfer from Escherichia coli K-12 under standard mating conditions.

Structure and function of conjugative pili: monoclonal antibodies as probes for structural variants of F pili

The lac-tra operon fusion plasmid pTG801 contains the known F plasmid DNA transfer (tra) genes required by Escherichia coli to elaborate functional F pili (T. Grossman and P. M. Silverman, J. Bacteriol. 171:650-656, 1989). Here, we show that these pili are actually structural variants of normal F pili and that the F plasmid must contain additional genes that affect pilus structure and function. We confirmed a previous report that two monoclonal antibodies that recognize epitopes at and near the amino terminus of F pilin do not decorate the sides of normal F pili, as determined by immunogold electron microscopy. However, both antibodies laterally decorated pTG801 pili. The epitope for one of the antibodies has been shown to include the amino-terminal acetyl group of F pilin, which must therefore also be present on pTG801 pilin. Normal antibody staining was restored to pTG801 pili when cells contained, in addition to pTG801, the compatible plasmid pRS31, which must therefore include at least one gene affecting F-pilus structure. One candidate, traD, was excluded as the sole such gene, since traD+ derivatives of a pTG801 strain still elaborated pili that could be laterally decorated with antibody. Moreover, although traD alone restored RNA bacteriophage R17 infectivity to pTG801 cells, as expected, it did not mimic pRS31 in restoring to pTG801 pili other characteristics of normal F pili. We conclude that pRS31 contains as yet uncharacterized genes required for elaboration of structurally normal F pili. Finally, we identified vesicular material, especially abundant in cultures of pTG801 transformants, that stained heavily with the anti-F-pilin monoclonal antibodies. This material may reflect the inner membrane pool of F pilin.