. 169:5152-5156, 1987) represents an artifact generated by nonspecific recombination of chromosomal DNA fragments. However, the amino terminus of this plasmid-encoded fusion product demonstrated significant homology to Escherichia coli ribosomal protein L6. By using a 458-bp PstI-HindHI fragment of recombinant pCT161/18 (representing the 5' end of the cloned gene), we isolated and characterized a C. trachomatis homolog of the ribosomal protein L6 gene of E. coli. Sequence analysis of an 1,194-bp EcoRI-SacI fragment that encodes chlamydial L6 (designated CtaL6e) revealed a 552-bp open reading frame comprising 183 amino acids and encodes a protein with a molecular weight of 19,839. Interestingly, complete gene homology between C. trachomatis serovars L2 and J, each of which exists as a single copy per genome, was observed. Expression of a plasmid-encoded gene product is dependent on the lac promoter, since no product was obtained if the open reading frame was oriented in opposition to the lac promoter. Immunblotting of purified ribosomes revealed functional, as well as antigenic, homology between the E. coli and C. trachomatis ribosomal L6 proteins.The obligate intracellular parasite Chlamydia trachomatis is an important pathogen associated with a broad spectrum of human disease (29). The unique life cycle of this prokaryote features two distinct developmental forms: the extracellular, infectious elementary body (EB) and the intracellular, metabolically active reticulate body (36). Elucidation of the regulatory controls governing its developmental stages is pivotal to understanding the biology of C. trachomatis.The initial EB attachment to the host cell represents a crucial step in this life cycle and appears to be necessary for successful invasion (36, 37). Attempts to study the attachment process have resulted in identification of two putative membrane protein adhesins of 18 and 31 kDa (9, 39). The cloning and sequencing of the 18-kDa surface-exposed adhesin has recently been reported from our laboratory (12). However, primary sequence comparisons of this protein with the SWISS-PROT protein data bank via BIONET have revealed significant homology of the N terminus of this binding protein with Escherichia coli L6 (EcoL6) and Bacillus stearothermophilus L10 (BstL6e) ribosomal proteins of the spc operon (13). In this report, we refer to the C. trachomatis L6 homolog or equivalent as CtaL6e on the basis of the nomenclature described by Shimmin and Dennis (30). (18) have characterized a chlamydial gene that encodes a protein homologous to ribosomal protein S1 in E. coli.The work presented here concerns elucidation of the relationship of the cloned 18-kDa putative binding protein to ribosomal proteins EcoL6 and BstL6e. We report the cloning, sequencing, and partial characterization of a gene for a ribosomal protein from C. trachomatis that is structurally and functionally homologous to ribosomal protein EcoL6. MATERIALS AND METHODSBacterial strains and media. C. trachomatis serovars L2 (L2/434/Bu), J (J/UW-36), D (D/...
We identified and sequenced a segment of Chlamydia trachomatis chromosomal DNA that shows homology to the Escherichia coli spc and distal region of the S10 ribosomal protein (r-protein) operons. Its sequence revealed a high degree of nucleotide and operon context conservation with the E. coli r-protein genes. The C. trachomatis spc operon contains the r-protein genes for L14, L24, L5, S8, L6, L18, S5, L15, and Sec Y along with the genes for r-proteins L16, L29, and S17 of the S10 operon. The two operons are separated by a 16-bp intragenic region which contains no transcription signals. However, a putative promoter for the transcription of the spc operon was found 162 nucleotides upstream of the CtrL14e start site; it revealed significant homology to the E. coli consensus promoter sequences. Interestingly, our results indicate the absence of any structure resembling an EcoS8 regulatory target site on C. trachomatis spc mRNA in spite of significant amino acid identity between E. coli and C. trachomatis r-proteins. Also, the intrinsic aminoglycoside resistance in C. trachomatis is unlikely to be mediated by CtrL6e since E. coli expressing CtrL6e remained susceptible to gentamicin (MIC < 0.5 ,ug/ml).Chlamydia trachomatis infections represent major public health problems in both developing and industrialized countries (30). Chlamydia species have evolved a complex and unique developmental cycle which involves two distinct forms: the small (0.2 to 0.3 ,um) extracellular, rigid elementary bodies and the large (1 ,um) intracellular, fragile reticulate bodies (44). The genetics of chlamydial regulation is largely undefined, mainly because of the lack of any convenient system for gene transfer and also because of the paucity of information about the signals and machinery that govern gene expression.Ribosomes constitute the protein-synthesizing machinery of both prokaryotes and eukaryotes. The entire prokaryotic ribosome comprises three rRNAs with sedimentation coefficients of 23S, 16S, and 5S and approximately 52 ribosomal proteins (r-proteins) that are organized into 19 different operons (26,33). Earlier attempts at characterizing the rRNA from Chlamydia species have met with some success. Tamura and Iwanaga (42) identified 21S, 16S, and 4S rRNA fractions in Chlamydia psittaci; of these, 21S and 16S were more predominant forms in reticulate bodies, whereas 4S predominated in the elementary bodies. Sarov and Becker found similar rRNA species in C. trachomatis (39). On the basis of their 16S rRNA gene sequence, chlamydiae have been identified as eubacterial in origin, related peripherally to planctomyces (45). Although a few other ribosomal determinants have been identified, r-protein gene organization and expression have not been well characterized (7-10, 20, 21). Interestingly, the organization and transcriptional regulation of r-protein operons appear to be well conserved among eubacteria; however, their regulation among evolutionary distant species remains unelucidated (15).Recently, we reported the cloning and sequen...
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