Developmental-form-specific DNA-binding proteins in Chlamydia spp

Detection of the Wolbachia-encoded DNA binding protein, HU beta, in mosquito gonads

Wolbachia are obligate intracellular bacteria that cause cytoplasmic incompatibility in mosquitoes. In an incompatible cross, eggs of uninfected females fail to hatch when fertilized by sperm from infected males. We used polyacrylamide gel electrophoresis and tandem mass spectrometry to identify Wolbachia proteins in infected mosquito gonads. These included surface proteins with masses of 25 and 18 kDa and the DNA binding protein, HU beta. Using reverse transcriptase polymerase chain reaction, we showed that the HU gene is transcribed in Wolbachia-infected Culex pipiens and Aedes albopictus mosquitoes. We sequenced HU genes from four Wolbachia strains and compared deduced protein sequences with additional homologs from the databases. Among the Rickettsiales, Wolbachia HU has distinct N- and C-terminal basic/acidic amino acid motifs as well as a pair of conserved, cysteine residues.

Quantitative proteomics reveals metabolic and pathogenic properties of Chlamydia trachomatis developmental forms

Chlamydia trachomatis is an obligate intracellular pathogen responsible for ocular and genital infections of significant public health importance. C. trachomatis undergoes a biphasic developmental cycle alternating between two distinct forms: the infectious elementary body (EB), and the replicative but non-infectious reticulate body (RB). The molecular basis for these developmental transitions and the metabolic properties of the EB and RB forms are poorly understood as these bacteria have traditionally been difficult to manipulate through classical genetic approaches. Using two-dimensional liquid chromatography - tandem mass spectrometry (LC/LC-MS/MS) we performed a large-scale, label-free quantitative proteomic analysis of C. trachomatis LGV-L2 EB and RB forms. Additionally, we carried out LC-MS/MS to analyse the membranes of the pathogen-containing vacuole ('inclusion'). We developed a label-free quantification approaches to measure protein abundance in a mixed-proteome background which we applied for EB and RB quantitative analysis. In this manner, we catalogued the relative distribution of > 54% of the predicted proteins in the C. trachomatis LGV-L2 proteome. Proteins required for central metabolism and glucose catabolism were predominant in the EB, whereas proteins associated with protein synthesis, ATP generation and nutrient transport were more abundant in the RB. These findings suggest that the EB is primed for a burst in metabolic activity upon entry, whereas the RB form is geared towards nutrient utilization, a rapid increase in cellular mass, and securing the resources for an impending transition back to the EB form. The most revealing difference between the two forms was the relative deficiency of cytoplasmic factors required for efficient type III secretion (T3S) in the RB stage at 18 h post infection, suggesting a reduced T3S capacity or a low frequency of active T3S apparatus assembled on a 'per organism' basis. Our results show that EB and RB proteomes are streamlined to fulfil their predicted biological functions: maximum infectivity for EBs and replicative capacity for RBs.

Characterization of integration host factor (IHF) binding upstream of the cysteine-rich protein operon (omcAB) promoter of Chlamydia trachomatis LGV serovar L2

Chlamydiae are bacterial parasites that carry out a distinct developmental cycle within host cells; however, the mechanisms by which these organisms regulate stage-specific gene expression are not known. We identified a DNA element located between nucleotide (nt) -135 and -90 upstream from the transcription start point of the late stage-specific CRP operon (omcAB) of Chlamydia trachomatis, to which a protein in extracts of chlamydiae harvested at 23 h after infection binds. A recombinant protein of C. trachomatis open reading frame (ORF) CT267, which is homologous to bacterial integration host factor (IHF) and the heat-unstable nucleoid protein (HU), bound to the same element and produced the same DNase I footprint as the protein in chlamydial extracts. Recombinant ORF CT267 protein bound with high affinity to the DNA element and induced a sharp bend in a DNA fragment containing the binding site, suggesting that ORF CT267 encodes a protein with IHF-like activity, and recombinant protein had a positive effect on in vitro transcription of the CRP operon. IHF-binding activity and IHF protein were detected in extracts of C. trachomatis during the early to intermediate phases of the late stage of the developmental cycle (between 17 and 30 h after infection), but were absent in the extreme late phase of the cycle and in the infectious form of chlamydiae. The presence of an IHF binding site upstream of the CRP operon and the presence of chlamydial IHF-like protein when late stage genes are transcribed suggests that the chlamydial IHF may play a role in stage-specific gene expression.

Genome sequence of an obligate intracellular pathogen of humans: Chlamydia trachomatis

Analysis of the 1,042,519-base pair Chlamydia trachomatis genome revealed unexpected features related to the complex biology of chlamydiae. Although chlamydiae lack many biosynthetic capabilities, they retain functions for performing key steps and interconversions of metabolites obtained from their mammalian host cells. Numerous potential virulence-associated proteins also were characterized. Several eukaryotic chromatin-associated domain proteins were identified, suggesting a eukaryotic-like mechanism for chlamydial nucleoid condensation and decondensation. The phylogenetic mosaic of chlamydial genes, including a large number of genes with phylogenetic origins from eukaryotes, implies a complex evolution for adaptation to obligate intracellular parasitism.

Purification, cloning, and preliminary characterization of a Spiroplasma citri ribosomal protein with DNA binding capacity

The rpsB-tsf-x operon of Spiroplasma citri encodes ribosomal protein S2 and elongation factor Ts, two components of the translational apparatus, and an unidentified X protein. A potential DNA-binding site (a 20-base pair (bp) inverted repeat sequence) is located at the 3' end of rpsB. Southwestern analysis of S. citri proteins, with a 30-bp double-stranded oligonucleotide probe (IRS), containing the 20-bp inverted repeat sequence and the genomic flanking sequences, detected an IRS-binding protein of 46 kDa (P46). P46 protein, which displays preferential affinity for the IRS, was purified from S. citri by a combination of affinity and gel filtration chromatographies. The native form of P46 seems to be homomultimeric as estimated by SDS-polyacrylamide gel electrophoresis analysis and gel filtration. A 3.5-kilobase pair S. citri DNA fragment comprising the P46 gene and flanking sequences was cloned and sequenced. Sequence analysis of this DNA fragment indicated that the P46 gene is located within the S10-spc operon of S. citri at the position of the gene coding for ribosomal protein L29 in the known S10-spc operons. The similarity between the N-terminal domain of P46 and the L29 ribosomal protein family and the presence of a 46-kDa IRS-binding protein in S. citri ribosomes indicated that P46 is the L29 ribosomal protein of S. citri. We suggest that P46 is a bifunctional protein with an L29 N-terminal domain and a C-terminal domain involved in IRS binding.

Sequence analysis and characterization of pOM1, a small cryptic plasmid from Butyrivibrio fibrisolvens, and its use in construction of a new family of cloning vectors for Butyrivibrios

As a preliminary step in the development of vector systems, we have isolated and begun to characterize small, cryptic plasmids from several strains of the rumen bacterium Butyrivibrio fibrisolvens. We present here the complete nucleotide sequence of Butyrivibrio plasmid pOM1, which was isolated from B. fibrisolvens Bu49. While it is very similar in size to the previously characterized Butyrivibrio plasmids pRJF1 and pRJF2, pOM1 exhibits a restriction pattern which is quite distinct. Analysis of sequence data reveals that pOM1 contains only two open reading frames of significant length (ORF1 and ORF2), both of which are required for self-replication and maintenance. The protein encoded in ORF1 shows homologies with Pre (plasmid recombination enzyme) proteins encoded in plasmids from gram-positive organisms such as Staphylococcus aureus, Streptococcus agalactiae, Lactobacillus plantarum, and Bacillus thuringiensis. The putative translation product of ORF2, on the other hand, resembles Rep (replication) proteins of a different group of gram-positive plasmids, for which the Staphylococcus plasmid pSN2 is a prototype. Unlike the other characterized-Butyrivibrio plasmids, pOM1 appears to replicate via a rolling-circle mechanism. Experimental evidence showing the presence of a single-stranded replication intermediate consistent with this mechanism is presented. pOM1 has been used in the construction of a new Escherichia coli-B. fibrisolvens shuttle vector, pSMerm1, which has been successfully used to introduce a cloned gene into B. fibrisolvens harboring the pRJF1 plasmid.

A developmental stage-specific histone H1 homolog of Coxiella burnetii

Two DNA-binding proteins have been detected in Coxiella burnetii by southwestern (DNA-protein) blotting. One of these, termed Hq1, is enriched in the small cell variant stage of the developmental cycle and displays compositional and primary amino acid sequence similarities to eukaryotic histone H1. C. burnetii appears to be another example of an intracellular parasite with morphologically distinct developmental forms whose nucleoid structure may be controlled by histone H1 homologs.

Functional domains of chlamydial histone H1-like protein

Chlamydial trachomatis is one of the few prokaryotic organisms known to contain proteins that bear amino acid similarity to eukaryotic histone H1. It is also appreciated that chlamydial histone-like proteins, designated Hc1 and Hc2, can bind DNA and are presumably involved in the condensation of infectious elementary bodies. However, there is no information on either the orientation of Hc1 and Hc2 or the mechanism of their DNA-protein and protein-protein interactions. Whereas the C-terminal domain of Hc1 between amino acids 63 and 125 shows best alignment with sea-urchin histone H1, and N-terminus between amino acids 1 and 62 is highly conserved among various chlamydial species, suggesting a bifunctional role for this unique protein. In order to delineate the regions responsible for the Hc1 characteristics, we have expressed these two fragments independently in Escherichia coli and studied the binding of double-stranded DNA to either whole Hc1 protein or its two termini. Our results support the role of the carboxyl portion in DNA-protein interaction, a function similar to its eukaryotic counterpart. Although this interaction initiates DNA condensation in the absence of the N-terminal domain, it is not sufficient to produce complete compaction. Intra- or inter-molecular protein-protein interactions may be necessary to achieve such an effect.

Purification of recombinant Chlamydia trachomatis histone H1-like protein Hc2, and comparative functional analysis of Hc2 and Hc1

The metabolically inactive developmental form of Chlamydia trachomatis, the elementary body, contains two very basic DNA-binding proteins with homology to eukaryotic histone H1. One of these, Hc1, is relatively well characterized and induces DNA condensation in vitro, whereas the other, Hc2, is functionally virtually uncharacterized. In this study we describe the purification of Hc2, and a detailed comparative functional analysis of Hc2 and Hc1 is presented. By gel shift assays and electron microscopy, marked differences in the nucleic acid-binding properties of Hc2 and Hc1 were observed. Furthermore, Hc2 was found to strongly inhibit translation and transcription in vitro. Our results imply that DNA condensation is not the only function of Hc2.

The 18-kilodalton Chlamydia trachomatis histone H1-like protein (Hc1) contains a potential N-terminal dimerization site and a C-terminal nucleic acid-binding domain

The Chlamydia trachomatis histone H1-like protein (Hc1) is a DNA-binding protein specific for the metabolically inactive chlamydial developmental form, the elementary body. Hc1 induces DNA condensation in Escherichia coli and is a strong inhibitor of transcription and translation. These effects may, in part, be due to Hc1-mediated alterations of DNA topology. To locate putative functional domains within Hc1, polypeptides Hc1(2-57) and Hc1(53-125), corresponding to the N- and C-terminal parts of Hc1, respectively, were generated. By chemical cross-linking with ethylene glycol-bis (succinic acid N-hydroxysuccinimide ester), purified recombinant Hc1 was found to form dimers. The dimerization site was located in the N-terminal part of Hc1 (Hc1(2-57)). Moreover, circular dichroism measurements indicated an overall alpha-helical structure of this region. By using limited proteolysis, Southwestern blotting, and gel retardation assays, Hc1(53-125) was shown to contain a domain capable of binding both DNA and RNA. Under the same conditions, Hc1(2-57) had no nucleic acid-binding activity. Electron microscopy of Hc1-DNA and Hc1(53-125)-DNA complexes revealed differences suggesting that the N-terminal part of Hc1 may affect the DNA-binding properties of Hc1.

Characterization of trimethoprim- and sulphisoxazole-resistant Chlamydia trachomatis

Trimethoprim and sulphisoxazole were used as selective agents in culture to isolate, by a stepwise procedure, a series of Chlamydia trachomatis L2 populations resistant to the cytotoxic effects of the drugs. Two trimethoprim-resistant populations, L2TriR-60 and L2TriR-100, and one sulphonamide-resistant population, L2SulfR-100, were characterized in more detail. In addition to being resistant to trimethoprim, L2TriR-60 was cross-resistant to methotrexate, sensitive to sulphisoxazole and displayed a ribonucleotide auxotrophy similar to that of its parental wild type, C. trachomatis L2. Surprisingly, L2TriR-100 and L2SulfR-100 appeared phenotypically identical. Both mutants were highly resistant to trimethoprim, sulphisoxazole, and methotrexate. In contrast to wild-type C. trachomatis L2, these populations were sensitive to 5-fluorouracil. L2TriR-100 and L2SulfR-100 were incapable of taking pyrimidine ribonucleotides from the host cell and no longer synthesized thymidine nucleotides de novo. The pyrimidine requirement of these mutants was met by salvaging host-cell uracil and thymidine, a property which can account for their drug-resistant characteristics. L2TriR-100 and L2SulfR-100 could also salvage adenine and guanine. Using L2TriR-100 as a starting stock, a mutant population resistant to the cytotoxic effects of trimethoprim and 5-fluorouracil (L2Tri/5-FU) was selected. L2Tri/5-FU was resistant to 5-fluorouracil because it had regained the capacity to take pyrimidine ribonucleotides from the host cell.

Chlamydiae and the biochemistry of intracellular parasitism

Despite the clinical and economic importance of chlamydial infections, many aspects of their basic biology, biochemistry and genetics have not been studied, and the metabolic relationships that exist between chlamydiae and their hosts are just beginning to be elucidated. While chlamydiae can biosynthesize some metabolic intermediates, they appear to be dependent on the host cell for others, which probably restricts them to an intracellular habitat.

Interaction of the Chlamydia trachomatis histone H1-like protein (Hc1) with DNA and RNA causes repression of transcription and translation in vitro

The 18 kDa histone H1-like protein from Chlamydia trachomatis (Hc1) is a DNA-binding protein thought to be involved in condensation of the chlamydial chromosome during late stages in the chlamydial life cycle. Expression of Hc1 in Escherichia coli results in an overall relaxation of DNA and severely affects DNA, RNA and protein synthesis. We have analysed the interaction of Hc1 with single-stranded DNA and RNA by Southwestern and Northwestern blotting. Furthermore, we show that purified, recombinant Hc1 dramatically affects transcription and translation in vitro at physiologically relevant concentrations. These results were found to coincide with the formation of condensed Hc1-DNA and Hc1-RNA complexes as revealed by agarose gel electrophoresis and electron microscopy. The implications of these results for possible functions of Hc1 in vivo are discussed.

Molecular mimicry and Chlamydia trachomatis infection of eukaryotic cells

A new experimental model for microbe-host-cell interaction is proposed in which a molecular mimic of heparan sulfate is used by Chlamydia to attach to the mammalian cell surface. A heparan-sulfate-like ligand, bound to the surface of Chlamydia, mediates infectivity by bridging the microorganism and mammalian cell receptors.

Diversity in the Chlamydia trachomatis histone homologue Hc2

Chlamydia trachomatis elementary bodies contain two developmentally expressed histone H1 homologues. An 18-kDa histone homologue, Hc1, is conserved among C. trachomatis serovars and C. psittaci. The other histone homologue, Hc2 (encoded by hctB), varies in size between C. trachomatis serovars but is present in reduced amounts or absent from C. psittaci. The variation in Hc2 size among C. trachomatis serovars was found to be due to internal deletions from a region of the hctB gene encoding lysine- and alanine-rich pentameric repeats.

Hc1-mediated effects on DNA structure: a potential regulator of chlamydial development

Chlamydiae are obligate intracellular bacteria which undergo a unique developmental cycle, alternating between non-replicative elementary bodies (EBs) and replicative reticulate bodies (RBs). The transition from RB to EB is characterized by condensation of the chromosome into a dense nucleoid structure. The chlamydial histone homologue Hc1 is sufficient to induce formation of a similar structure in Escherichia coli. High-level Hc1 expression in E. coli is self-limiting and down-regulates transcription, translation, and replication at concentrations similar to those observed in chlamydial elementary bodies. Expression of Hc1 at sub-structural levels may have specific regulatory functions through its interaction with chromosomal DNA. In E. coli this is reflected in a dramatic shift in the pattern of gene expression. The differential expression of the outer membrane porin proteins OmpC and OmpF and analysis of lacZ fusions with promoter regions sensitive to supercoiling suggests that low-level Hc1 expression results in a net relaxation of chromosomal DNA. Topological analysis of plasmid DNA from both E. coli and Chlamydia trachomatis supports a decrease in superhelicity preceding nucleoid formation. In vitro analysis of purified Hc1-DNA interactions supports preferential binding based upon DNA conformation. These results suggest a dual role in which Hc1-mediated changes in gene expression may precede metabolic inactivity.

Molecular cloning and expression of hctB encoding a strain-variant chlamydial histone-like protein with DNA-binding activity

Two DNA-binding proteins with similarity to eukaryotic histone H1 have been described in Chlamydia trachomatis. In addition to the 18-kDa histone H1 homolog Hc1, elementary bodies of C. trachomatis possess an antigenically related histone H1 homolog, which we have termed Hc2, that varies in apparent molecular mass among strains. We report the molecular cloning, expression, and nucleotide sequence of the hctB gene encoding Hc2 and present evidence for in vivo DNA-binding activity of the expressed product. Expression of Hc2 in Escherichia coli induces a compaction of bacterial chromatin that is distinct from that observed upon Hc1 expression. Moreover, isolated nucleoids from Hc2-expressing E. coli exhibit markedly reduced sensitivity to DNase I. These properties of Hc2 are consistent with a postulated role in establishing the nucleoid structure of elementary bodies.

Identification of an early-stage gene of Chlamydia psittaci 6BC

Chlamydiae are parasitic bacteria characterized by a temporally regulated developmental cycle. In the early stage of the cycle, metabolically inert elementary bodies reorganize to dividing reticulate bodies, a process about which little is known. The purpose of this investigation was to identify and clone chlamydial genes that are expressed preferentially during the early stage of the developmental cycle of Chlamydia psittaci 6BC. Several potential early genes were cloned with highly radioactive, host-free-generated RNA probes to screen a genomic library. One clone appeared to encode a gene that was particularly well expressed at 1 h postinfection. In further characterization, we found that it encodes two complete open reading frames and one partial open reading frame of 370 codons. The partial open reading frame, designated gltX, is very similar to bacterial glutamyl-tRNA synthetases and was demonstrated to be transcribed in vivo at 24 h postinfection by primer extension analysis. A lysine-rich open reading frame (LRO) of 117 codons was found upstream and divergent from gltX. The LRO lacks homology to known proteins, and we were unable to demonstrate that it is transcribed in vivo. The third open reading frame, of 182 codons, was found to be convergent with and partially overlap the LRO. It was confirmed to be preferentially expressed within the first 1.5 h of infection by Northern (RNA) blot analysis and was designated the early upstream open reading frame (EUO). Like the LRO, the EUO is not homologous to known proteins. A major potential transcription start site of the EUO was identified by primer extension analysis. However, the sequence upstream of the site does not closely resemble the consensus recognition sequences of bacterial sigma factors even though it is AT rich. The EUO is the first chlamydial gene specific to the early stage to be cloned and sequenced.

In vitro transcription in Chlamydia psittaci and Chlamydia trachomatis

Extracts of Chlamydia psittaci and Chlamydia trachomatis were used to transcribe molecularly cloned chlamydial genes in vitro. The extracts were prepared by lysing reticulate bodies, obtaining the 10,000 x g centrifugation pellet, and eluting RNA polymerase from the pellet by treatment with 2M KCl to yield a fraction designated SS2. Some in vitro transcription was initiated from non-chlamydial promoters and a small amount of transcription was from endogenous DNA template in SS2. However, optimal transcription from exogenous templates required chlamydial promoter sequences, and primer extension analysis indicated that chlamydia promoter-specific in vitro transcription was initiated from the same start sites recognized in vivo. A monoclonal antibody that was generated against Escherichia coli sigma 70 and which immunologically cross-reacts with C. trachomatis sigma 66 inhibited in vitro transcription of vector and cloned chlamydial DNA, suggesting that transcriptional initiation in the SS2 fraction is mediated by sigma 66. An in vitro transcription assay based on detection of transcripts of specific lengths was applied to the chlamydial system; this assay and others described here should be useful in defining chlamydial promoters and other transcriptional regulatory elements.

Interaction between the Chlamydia trachomatis histone H1-like protein (Hc1) and DNA

The gene encoding the Chlamydia trachomatis histone H1-like protein (Hc1) from serovar L2 was cloned into Escherichia coli by use of expression vector pET11d. In this vector, transcription of the gene is under the control of a bacteriophage T7 promoter, and T7 RNA polymerase is inducible in the host. Following induction, the E. coli cells were lysed gently. Gel filtration of the lysate revealed comigration of DNA and Hc1 in the voided volume. Electron microscopy revealed the DNA to be complexed with protein in large aggregates, often in the form of spherical bodies. Purified recombinant Hc1 maintained its DNA-binding capacity and was able at high concentrations to form condensed aggregates with DNA (one molecule of Hc1 per base pair) independently of the form or size of the DNA but with a slight preference for supercoiled DNA. Hc1 alone is thus able to package DNA into condensed spherical bodies.

Properties of purified sporlets produced by spoII mutants of Bacillus subtilis

A number of abortively disporic spoII mutants of Bacillus subtilis released their forespore compartments (termed stage II sporlets) after mother cell lysis during sporulation in nutrient exhaustion or resuspension media. Stage II sporlets were viable and contained levels of ATP and a number of enzymes similar to those in cells 2 to 3 h after sporulation. However, stage II sporlets carried out essentially no macromolecular synthesis, a result suggesting that they were in a quiescent state. The nucleoid of these quiescent stage II sporlets was significantly condensed relative to that in the original vegetative cells, as was previously found to take place 1 to 2 h after initiation of sporulation (B. Setlow, N. Magill, P. Febbroriello, L. Nakhimousky, D. E. Koppel, and P. Setlow, J. Bacteriol. 173:6270-6278, 1991). Stage II sporlets may be a useful model system for analysis of forespore properties early in stage II of sporulation.

Construction of physical and genetic maps of Chlamydia trachomatis serovar L2 by pulsed-field gel electrophoresis

We constructed the physical map of Chlamydia trachomatis serovar L2 by using three restriction endonucleases, NotI (GC[GGCCGC), SgrAI (C(A/G)[CCGG(T/G)G), and Sse8387I (CCTGCA[GG), and we analyzed the fragments by pulsed-field gel electrophoresis. A total of 25 restriction endonuclease sites and 13 genes and/or operons were located on the map. The genome size was determined to be 1,045 kb. Neither highly transcribed chlamydia genes nor developmental cycle-specific genes were clustered on the genome.

Nucleoid condensation in Escherichia coli that express a chlamydial histone homolog

Chlamydial cell types are adapted for either extracellular survival or intracellular growth. In the transcriptionally inert elementary bodies, the chromosome is densely compacted; in metabolically active reticulate bodies, the chromatin is loosely organized. Condensation of the chlamydial nucleoid occurs concomitant with expression of proteins homologous to eukaryotic histone H1. When the Chlamydia trachomatis 18-kilodalton histone homolog Hc1 is expressed in Escherichia coli, a condensed nucleoid structure similar to that of chlamydiae is observed with both light and electron microscopy. These results support a role for Hc1 in condensation of the chlamydial nucleoid.

Eukaryotic cell components that bind to chlamydial elementary bodies: the histones

HeLa-cell-membrane fractions isolated by sonication as used previously to identify chlamydial adhesins were examined by a blotting technique for binding chlamydial elementary bodies (EB). One HeLa cell protein with apparent molecular mass of 32 kDa was found to bind native EB. A monoclonal antibody (mAb) raised against this chlamydial binding host-cell protein reacted with eucaryotic histones. Histone fractions were capable of binding EB in an ELISA assay and histone H1 was identified as the chlamydial-binding host cell protein in the Hela cell membrane fraction. Probing with specific mAbs against histone H3 and DNA confirmed that chromatin components were present in the host-cell membrane extract. These data suggest that the HeLa-cell-binding chlamydial proteins were previously identified by their reaction with chromatin and not with membrane components.

A developmentally regulated chlamydial gene with apparent homology to eukaryotic histone H1

We have developed a method for the isolation of genes whose expression is developmentally regulated from the murine strain of Chlamydia trachomatis. Here we describe the identification of two developmental stage-specific genes, one of which is predicted to encode a 26-kDa lysine- and alanine-rich protein that appears to be homologous to several eukaryotic histone H1 proteins. A substantial proportion of this homology relates to its distinctive amino acid composition. No sequence homology was observed between this protein and other bacterial "histone-like" chromosomal proteins, but homology does exist with two other recently described prokaryotic proteins. The protein is expressed late in chlamydial development, during the transition from reticulate bodies to elementary bodies. The basic nature of the protein predicts that it could bind DNA, and Southwestern blotting experiments confirm this finding. These properties are consistent with a role either in the regulation of late gene expression or in the compaction of the chlamydial genome.

Purification and N-terminal amino acid sequences of Chlamydia trachomatis histone analogs

DNA-binding proteins specific to Chlamydia trachomatis elementary bodies have been described and recently characterized as procaryotic histone analogs. I have developed an affinity purification procedure for the 18-kDa histone analog, Hc1, based on its affinity for polyanions. The availability of highly purified Hc1 has allowed for determination of its N-terminal amino acid sequence and should prove useful in studies of its biological function. The variable C. trachomatis histone analog not obtained by this procedure was electrophoresed onto Immobilon paper for sequencing. The N terminus of the variable histone was conserved among C. trachomatis serotypes L2, D, and B and was distinct from that of Hc1.

A chlamydial plasmid is differentially transcribed during the life cycle of Chlamydia trachomatis

A 7.5-kb cryptic plasmid is found in all serotypes of the obligate intracellular parasite, Chlamydia trachomatis. Although at least nine open reading frames are apparent from sequence analysis of plasmid DNA, only a small region of approximately 500 bp has been consistently shown to be transcriptionally active by Northern blot analysis. In this study, transcription was analyzed using a host-free system in which RNA synthesized by chlamydiae isolated from host cells was hybridized to different regions of the plasmid. The results suggest that fragments corresponding to all open reading frames are transcribed, but at varied relative levels depending upon the stage of the life cycle. The hybridization patterns also suggested a net chemical degradation of plasmid-specified RNA in a 3' to 5' direction.

Identification and nucleotide sequence of a developmentally regulated gene encoding a eukaryotic histone H1-like protein from Chlamydia trachomatis

A lambda gt11 recombinant library of Chlamydia trachomatis serovar L2 chromosomal DNA was screened with a 29-mer synthetic oligonucleotide specific to the N-terminal amino acids of a predominant 18-kDa chlamydial protein. One recombinant clone, designated lambda gt11/L2/RKA10, was selected on the basis of its strong hybridization signal. Restriction endonuclease analysis and complete nucleotide sequencing of the recombinant revealed a 2,633-bp insert containing one complete open reading frame (ORF2) and two partial ORFs (ORF1 and ORF3). The deduced amino acid sequence of ORF2 matched perfectly at its N-terminal end with the derived amino acid sequence. The 375-bp ORF is capable of encoding a protein comprising 125 amino acids with a molecular mass of 13,689. A sequence compatible with a Shine-Dalgarno ribosome-binding site was located 9 bp upstream from the initiation codon, while the sequence distal to ORF2 revealed a rho-independent terminator. The protein, designated CTH1, possesses an estimated pI of 10.71 due to its high lysine content. This highly basic protein contains no tryptophan or phenylalanine. A protein data base search identified significant homology between CTH1 and painted sea urchin histone H1. Northern (RNA) blot analysis of Chlamydia-infected host cells demonstrated transcripts at 12 h postinfection. The recombinant plasmid encoding ORF2 expressed a gene product of approximately 18 kDa, similar to the native chlamydial protein as analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This protein appears to represent one of the few eukaryotic histonelike proteins described to date in prokaryotes.

Chlamydia trachomatis developmentally regulated protein is homologous to eukaryotic histone H1

Chlamydiae are prokaryotic obligate intracellular parasites that undergo a biphasic life cycle involving an infectious, extracellular form known as elementary bodies and an intracellular, replicating form termed reticulate bodies. We have purified from Chlamydia trachomatis a very basic elementary body-specific protein with an apparent molecular mass of 18 kDa, determined its N-terminal amino acid sequence, and cloned the encoding gene. Sequence analysis of the cloned gene revealed some remarkable properties for its expressed product, including a high lysine content (29%), a correspondingly high pI, and significant homology to the H1 class of eukaryotic histones. Furthermore, a monoclonal antibody to this chlamydial histone analog, termed Hc1, displayed immunoblot and antinuclear specificity suggestive of cross-reactivity to H1 histones. The gene was expressed only during the late stages of the chlamydial life cycle concomitant with the reorganization of chlamydial reticulate bodies into elementary bodies, suggesting that the Hc1 protein plays a role in the condensation of chlamydial chromatin during intracellular differentiation.

Interaction of chlamydiae and host cells in vitro

The obligately intracellular bacteria of the genus Chlamydia, which is only remotely related to other eubacterial genera, cause many diseases of humans, nonhuman mammals, and birds. Interaction of chlamydiae with host cells in vitro has been studied as a model of infection in natural hosts and as an example of the adaptation of an organism to an unusual environment, the inside of another living cell. Among the novel adaptations made by chlamydiae have been the substitution of disulfide-bond-cross-linked polypeptides for peptidoglycans and the use of host-generated nucleotide triphosphates as sources of metabolic energy. The effect of contact between chlamydiae and host cells in culture varies from no effect at all to rapid destruction of either chlamydiae or host cells. When successful infection occurs, it is usually followed by production of large numbers of progeny and destruction of host cells. However, host cells containing chlamydiae sometimes continue to divide, with or without overt signs of infection, and chlamydiae may persist indefinitely in cell cultures. Some of the many factors that influence the outcome of chlamydia-host cell interaction are kind of chlamydiae, kind of host cells, mode of chlamydial entry, nutritional adequacy of the culture medium, presence of antimicrobial agents, and presence of immune cells and soluble immune factors. General characteristics of chlamydial multiplication in cells of their natural hosts are reproduced in established cell lines, but reproduction in vitro of the subtle differences in chlamydial behavior responsible for the individuality of the different chlamydial diseases will require better in vitro models.

Developmental-stage-specific plasmid supercoiling in Chlamydia trachomatis

Chlamydia trachomatis elementary body (EB) and reticulate body (RB) developmental stages have polymorphic plasmid DNA. Several plasmid forms separated by gel electrophoresis were identified as topoisomers by treatment with topoisomerase I. Among these topoisomers was one form unique to EBs and one form unique to RBs. The unique EB plasmid topoisomer was characterized as highly supercoiled, on the basis of band migrations by gel electrophoresis and its appearance by electron microscopy. The unusual physical state of this topoisomer was probably mediated, in part, by DNA-specific structural proteins. The unique RB plasmid topoisomer was a supercoiled form of lower superhelical density than the other identified topoisomers. Developmental-stage-specific differences in super-helical density of plasmid DNA suggest cause-and-effect relationships between DNA topology and metabolic activity in RBs and metabolic quiescence in EBs.

Characterization and identification of early proteins in Chlamydia trachomatis serovar L2 by two-dimensional gel electrophoresis

The synthesis of early proteins from Chlamydia trachomatis serovar L2 was analyzed by two-dimensional gel electrophoresis. By pulse-label experiments, the synthesis of seven proteins was observed at 2 to 8 h postinfection before the major outer membrane protein was detected at 8 to 10 h after infection. The early proteins were synthesized throughout the 30-h period investigated, but the synthesis of three proteins of 75, 62, and 45 kilodaltons decreased from 26 to 30 h postinfection. Pulse-chase analysis showed that the signals from the same three proteins declined 26 to 30 h after infection. Three of the early proteins were identified as the S1 ribosomal protein, the GroEL-like protein, and DnaK-like protein, respectively.

DNA-binding proteins in cells and membrane blebs of Neisseria gonorrhoeae

Naturally elaborated membrane bleb fractions BI and BII of Neisseria gonorrhoeae contain both linear and circular DNAs. Because little is known about the interactions between DNA and blebs, studies were initiated to identify specific proteins that bind DNA in elaborated membrane blebs. Western immunoblots of whole-cell and bleb proteins from transformation-competent and DNA-uptake-deficient (dud) mutants were probed with single- or double-stranded gonococcal DNA, pBR322, or synthetic DNA oligomers containing intact or altered gonococcal transformation uptake sequences. The specificity and sensitivity of a nonradioactive DNA-binding protein assay was evaluated, and the assay was used to visualize DNA-protein complexes on the blots. The complexes were then characterized by molecular mass, DNA-binding specificity, and expression in bleb fractions. The assay effectively detected blotted DNA-binding proteins. At least 17 gonococcal DNA-binding proteins were identified; unique subsets occurred in BI and BII. Certain DNA-binding proteins had varied affinities for single- and double-stranded DNA, and the intact transformation uptake sequence competitively displaced the altered sequence from a BI protein at 11 kilodaltons (kDa). A dud mutant, strain FA660, lacked DNA-binding activity at the 11-kDa protein in BI. The segregation of DNA-binding proteins within BI and BII correlates with their distinct protein profiles and suggests that these vesicles may play different roles. Although the DNA-binding proteins expressed in BII may influence the nuclease-resistant export of plasmids within BII vesicles, the BI 11-kDa protein may bind transforming DNA.