N-Methyl transferase of Streptomyces erythraeus that confers resistance to the macrolide-lincosamide-streptogramin B antibiotics: amino acid sequence and its homology to cognate R-factor enzymes from pathogenic bacilli and cocci

A repeated decapeptide motif in the C-terminal domain of the ribosomal RNA methyltransferase from the erythromycin producer Saccharopolyspora erythraea

Re-analysis of the primary structure of the ribosomal RNA N-methyltransferase that confers self-resistance on the erythromycin-producing bacterium Saccharopolyspora erythraea has confirmed the presence of a C-terminal domain containing extensive repeat sequences. Nine tandem repeats can be discerned, with a decapeptide consensus sequence GGRx(H/R)GDRRT, although no single residue is wholly invariant. This highly polar, potentially flexible domain, which is predicted to adopt either a random coil or a structure with beta turns, has a counterpart in the erythromycin methyltransferase of an erythromycin-producing species of Arthrobacter. It also significantly resembles a portion of the C-terminal region of the eukaryotic protein nucleolin, which is unusually rich in dimethylarginine and glycine, and which is also predicted to behave as a random coil in solution. This resemblance, despite the very different roles of these proteins in ribosome biogenesis, strengthens the idea that in both rRNA methyltransferases and nucleolin these C-terminal sequences might contribute to rRNA binding.

Nucleotide sequence of Streptomyces fradiae transposable element Tn4556: a class-II transposon related to Tn3

The first transposable element to be isolated from Streptomyces fradiae, Tn4556, was completely sequenced; the total of 6625 bp have an overall G + C composition of 68%. Computer-aided analysis of this sequence reveals the location of nine open reading frames (ORFs). Several of these ORFs, numbers 1, 2, and 7, contain ribosome-binding sites (RBS) near their putative translation-initiation sites, which share identity with the consensus RBS sequences of Escherichia coli and Bacillus subtilis. ORF1 potentially encodes an 892-amino acid (aa) protein and this deduced aa sequence shares 61% identity with that of the transposase encoded by the tnpA gene of Tn3. Three other ORFs, 2, 3 and 5, potentially encode proteins which are similar in size to the resolvase protein encoded by the Tn3 gene tnpR; however, none of the protein products deduced from these ORF share extensive aa sequence identity with other resolvase proteins.

Cloning of genes governing the deoxysugar portion of the erythromycin biosynthesis pathway in Saccharopolyspora erythraea (Streptomyces erythreus)

Genes that govern the formation of deoxysugars or their attachment to erythronolide B and 3 alpha-mycarosyl erythronolide B, intermediates of the biosynthesis of the 14-membered macrolide antibiotic erythromycin, were cloned from Saccharopolyspora erythraea (formerly Streptomyces erythreus). Segments of DNA that complement the eryB25, eryB26, eryB46, eryC1-60, and eryD24 mutations blocking the formation of erythronolide B or 3 alpha-mycarosyl erythronolide B, when cloned in Escherichia coli-Streptomyces shuttle cosmids or plasmid vectors that can transform S. erythraea, were located in a ca. 18-kilobase-pair region upstream of the erythromycin resistance (ermE) gene. The eryC1 gene lies just to the 5' side of ermE, and one (or possibly two) eryB gene is approximately 12 kilobase pairs farther upstream. Another eryB gene may be in the same region, while an additional eryB mutation appears to be located elsewhere. The eryD gene lies between the eryB and eryC1 genes and may regulate their function on the basis of the phenotype of an EryD- mutant.

Molecular characterization of a gene from Saccharopolyspora erythraea (Streptomyces erythraeus) which is involved in erythromycin biosynthesis

A 7.3 kbp DNA fragment, encompassing the erythromycin (Em) resistance gene (ermE) and a portion of the gene cluster encoding the biosynthetic genes for erythromycin biosynthesis in Saccharopolyspora erythraea (formerly Streptomyces erythraeus) has been cloned in Streptomyces lividans using the plasmid vector pIJ702, and its nucleotide sequence has been determined using a modified dideoxy chain-termination procedure. In particular, we have examined the region immediately 5' of the resistance determinant, where the tandem promoters for ermE overlap the promoters for a divergently transcribed coding sequence (ORF). Disruption of this ORF using an integrational pIJ702-based plasmid vector gave mutants which were specifically blocked in erythromycin biosynthesis, and which accumulated 3-O-alpha-L-mycarosylerythronolide B: this behaviour is identical to that of previously described eryC1 mutants. The eryC1-gene product, a protein of subunit Mr 39,200, is therefore involved either as a structural or as a regulatory gene in the formation of the deoxyamino-sugar desosamine or in its attachment to the macrolide ring.

Cloning and hybridization analysis of ermP, a macrolide-lincosamide-streptogramin B resistance determinant from Clostridium perfringens

The erythromycin resistance determinant from Clostridium perfringens CP592 was cloned and shown to be expressed in Escherichia coli. The resultant plasmid, pJIR122 (7.9 kilobase pairs [kb]), was unstable since in both recA+ and recA E. coli hosts spontaneous deletion of 2.7 kb, including the erythromycin resistance determinant, was observed. Subcloning, as well as deletion analysis with BAL 31, localized the erythromycin resistance gene (ermP) to within a 1.0-kb region of pJIR122. A 0.5-kb fragment internal to ermP was 32P labeled and used as an ermP-specific probe in DNA hybridization experiments which used target DNA prepared from representatives of each of the known erm classes and also from erythromycin-resistant isolates of a variety of clostridial species. Hybridizing sequences were detected in DNA from several Clostridium difficile isolates and a Clostridium paraputrificum strain; however, ermP was not widespread in erythromycin-resistant C. perfringens isolates. The ermP determinant hybridized to, and shared significant restriction identity with, the ermB class gene from the streptococcal plasmid pAM beta 1. No hybridization was detected with the other six hybridization classes of erm determinants.

Methylation of 23S rRNA caused by tlrA (ermSF), a tylosin resistance determinant from Streptomyces fradiae

Ribosomes from Streptomyces griseofuscus expressing tlrA, a resistance gene isolated from the tylosin producer Streptomyces fradiae, are resistant to macrolide and lincosamide antibiotics in vitro. The tlrA product was found to be a methylase that introduces two methyl groups into a single base within 23S rRNA, generating N6,N6-dimethyladenine at position 2058. This activity is therefore similar to the ermE resistance mechanism in Saccharopolyspora erythraea (formerly Streptomyces erythraeus).

Intergeneric conjugation between Escherichia coli and Streptomyces species

We have constructed Escherichia coli-Streptomyces shuttle plasmids which are capable of conjugal transfer from E. coli to Streptomyces spp. These plasmids contained the pBR322 and pIJ101 origins of replication and the RK2 (IncP) origin of transfer. The transfer of plasmid was specifically dependent the presence of a 760-base-pair, cis-acting, oriT-containing fragment and on RP4 (IncP) functions supplied in trans. Conditions of mating and selection of exconjugants were analyzed with Streptomyces lividans as recipient. Plasmid transfer to other Streptomyces species was also demonstrated.

Identification of a gene required for the terminal step in erythromycin A biosynthesis in Saccharopolyspora erythraea (Streptomyces erythreus)

We have identified a transcription unit in the ermE region of the chromosome of the erythromycin (Er)-producing bacterium Saccharopolyspora erythraea (Streptomyces erythreus) that is briefly switched on at about the time that macrolide production commences. Disruption of the transcription unit, herein designated eryG, by insertion of an integrational plasmid vector, caused a block at the terminal step in the biosynthesis of erythromycin, the conversion of erythromycin C to A by O-methylation.

Codon usage as a reason for unsuccessful search for amber-suppressor mutants in Streptomyces lividans?

An amber mutation was created in the CAT gene of plasmid vector pACYC184 and this modified plasmid was fused with theStreptomycesvector pIJ702 for use as an indicator for the identification ofStreptomycesstrains carrying nonsense suppressor tRNA mutations. The resulting hybrid plasmid pGM1109 was introduced into the chloramphenicol-sensitive mutant M252 ofStreptomyces lividans. Chloramphenicol-resistant colonies were isolated and characterized. None of them was a nonsense suppressor mutant. The failure to obtain such mutants is discussed on the basis of codon usage in streptomycetes.

Complete nucleotide sequence of the Streptomyces lividans plasmid pIJ101 and correlation of the sequence with genetic properties

The complete nucleotide sequence of the multicopy Streptomyces plasmid pIJ101 has been determined and correlated with previously published genetic data. The circular DNA molecule is 8,830 nucleotides in length and has a G+C composition of 72.98%. The use of a computer program, FRAME, enabled identification in the sequence of seven open reading frames, four of which, tra (621 amino acids [aa]), spdA (146 aa), spdB (274 aa), and kilB (177 aa), appear to be genes involved in plasmid transfer. At least two of the above genes are predicted to be transcribed by known promoters that are regulated in trans by the products of the korA (241 aa) and korB (80 aa) loci on the plasmid. The segment of the plasmid capable of autonomous replication contains one large open reading frame (rep; 450 aa) and a noncoding region presumed to be the origin of replication. Four other small (less than 90 aa) open reading frames are also present on the plasmid, although no function can be attributed to them. The sequence of the pIJ101 replication segment present in several widely used cloning vectors (e.g., pIJ350 and pIJ702) has also been determined, so that the complete nucleotide sequences of these vectors are now known.

The use of a chromosome integration vector to map erythromycin resistance and production genes in Saccharopolyspora erythraea (Streptomyces erythraeus)

The thiostrepton-resistance-conferring plasmid pIJ702 was integrated into the ermE region of the chromosome of erythromycin (Er)-producing bacterium Saccharopolyspora erythraea (Streptomyces erythraeus) by single, reciprocal (Campbell) recombination between DNA cloned in the vector and homologous nucleotide sequences in the chromosome. Genetic mapping experiments by conjugational transfer were used to establish that the ErR gene, ermE, was located close to the Er-production loci eryA34 and eryB25.

Nucleotide sequence of Acinetobacter baumannii aphA-6 gene: evolutionary and functional implications of sequence homologies with nucleotide-binding proteins, kinases and other aminoglycoside-modifying enzymes

A new kanamycin-resistance gene, detected in Acinetobacter baumannii and designated aphA-6, was sequenced. It specifies a 30319 Dalton 3'-aminoglycoside phosphotransferase (APH(3'] that mediates resistance to kanamycin and structurally related aminoglycosides, including amikacin. Pairwise comparisons of the six types of APH(3') so far detected in human pathogens (types I, II, III and VI) and in amino-glycoside-producing microorganisms (types IV and V), confirm that APH(3') enzymes have diverged from a common ancestor. Three highly retained motifs (1: V--HGD----N; 2: G--D-GR/K-G and 3: D--K/R--Y/F---LDE) located in the C-terminal part of the enzymes were defined. Screening of protein sequence data bases fore each of these motifs revealed that motifs 1 and 2 are both found in nucleotide-binding phosphotransferases associated with a variety of biological processes, namely adenylate kinase, viral oncogenic protein kinases, elongation factors, Na+/K+-transporting ATPase, myosin and antibiotic-modifying enzymes. Motif 2 probably corresponds to the MgATP binding site, while motifs 3 and 1 could be involved in the splitting of the phosphodiester bond and in the phosphate transfer, respectively. Moreover, an additional motif, almost invariably centrally located, was found in all aminoglycoside-modifying enzymes. The occurrence of this motif, possibly a recombination site which would have allowed the association of units of separate functions, is compatible with a modular concept for the structure of aminoglycoside-modifying enzymes.

Evidence for natural gene transfer from gram-positive cocci to Escherichia coli

High-level resistance to macrolide-lincosamide-streptogramin type B (MLS) antibiotics in Escherichia coli BM2570 is due to the presence on the conjugative plasmid pIP1527 of the MLS resistance determinant ermBC, which is almost identical to the erm genes previously described in plasmid pAM77 from Streptococcus sanguis (ermAM) and in transposon Tn917 from Enterococcus faecalis (ermB). This gene and its regulatory region are located downstream from the insertion sequence IS1. The 23S rRNA methylase encoded by pIP1527 differs by three and six amino acids from those encoded by Tn917 and pAM77, respectively. Unlike the streptococcal elements which confer the inducible MLS phenotype, the ermBC gene is expressed constitutively in E. coli and Bacillus subtilis, due to several mutations in the regulatory region. Transcription of the ermBC gene starts from three different sites following three overlapping promoters which function in both E. coli and B. subtilis. Promoters P2 and P3 are located within the region homologous to pAM77 and Tn917, and P1 is a hybrid promoter constituted by -35 and -10 sequences located at the end of IS15 and in the streptococcal region, respectively. These results constitute evidence for the recent in vivo transfer from Streptococcus spp. to E. coli. This transfer could have been mediated by transposons such as Tn917 or Tn1545 from Streptococcus pneumoniae, which also bears an MLS determinant that is homologous to ermB. We speculate that the insertion sequences IS15 and IS1 could have played a role in the expression and dissemination of ermBC, which has been found in numerous strains of enterobacteria.

Translational attenuation control of ermSF, an inducible resistance determinant encoding rRNA N-methyltransferase from Streptomyces fradiae

An inducible resistance determinant, ermSF, from the tylosin producer Streptomyces fradiae NRRL 2338 has been cloned, sequenced, and shown to confer inducible macrolide-lincosamide-streptogramin B resistance when transferred to Streptomyces griseofuscus NRRL 23916. From mapping studies with S1 nuclease to locate the site of transcription initiation, the ermSF message contains a 385-nucleotide 5' leader sequence upstream from the 960-nucleotide major open reading frame that encodes the resistance determinant. On the basis of the potential secondary structure that the ermSF leader can assume, a translational attenuation model similar to that for ermC is proposed. The model is supported by mutational analysis involving deletions in the proposed attenuator. By analysis with restriction endonucleases, ermSF is indistinguishable from the tlrA gene described by Birmingham et al. (V. A. Birmingham, K. L. Cox, J. L. Larson, S. E. Fishman, C. L. Hershberger, and E. T. Seno, Mol. Gen. Genet. 204:532-539, 1986) which comprises one of at least three genes from S. fradiae that can confer tylosin resistance when subcloned into S. griseofuscus. When tested for inducibility, ermSF appears to be strongly induced by erythromycin, but not by tylosin.

Characterization of the promoter, signal sequence, and amino terminus of a secreted beta-galactosidase from "Streptomyces lividans"

The gene for a secreted 130-kilodalton beta-galactosidase from "Streptomyces lividans" has been cloned, its promoter, signal sequence, and amino terminal region have been localized, and their nucleotide sequence has been determined. The signal sequence extends over 56 amino acids and shows the characteristic-features of signal sequences, including a hydrophilic amino terminus followed by a hydrophobic core near the signal cleavage site. The secretion of beta-galactosidase depends on the presence of the signal sequence. beta-Galactosidase is the major protein in culture supernatants and extracts of strains expressing the cloned beta-galactosidase gene and represents a valuable tool in the study of protein secretion in Streptomyces spp.

Genetic characterization of a Clostridium difficile erythromycin-clindamycin resistance determinant that is transferable to Staphylococcus aureus

The transferable macrolides-lincosamides-streptogramin B (MLS) resistance determinant of clinical isolates of Clostridium difficile, designated ermZ, has been shown to share homology with ermB, which is associated with Staphylococcus aureus transposon Tn551. Homology within Tn551 was confined to less than or equal to 1.3 kilobases, whereas no homology could be demonstrated between Tn551 sequences external to ermB and MLS-resistant C. difficile. Transfer of ermZ from C. difficile to S. aureus was achieved by means of the filter mating technique, suggesting that (conjugative?) intergeneric exchange between clostridia and staphylococci may also occur in nature. S. aureus transcipients were shown to contain additional DNA from C. difficile besides ermZ. This additional DNA appeared to be present in MLS-susceptible C. difficile and might form part of an as yet undemonstrated insertion sequence element associated with ermZ of resistant strains.

Nucleotide sequence of the streptothricin acetyltransferase gene from Streptomyces lavendulae and its expression in heterologous hosts

The nucleotide sequence of the streptothricin acetyltransferase (STAT) gene from streptothricin-producing Streptomyces lavendulae predicts a 189-amino-acid protein of molecular weight 20,000, which is consistent with that determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified enzyme. The amino acid composition and the NH2-terminal sequence determined by using the purified protein are in good agreement with those predicted from the nucleotide sequence, except for the absence of the NH2-terminal methionine in the mature protein. High-resolution S1 nuclease protection mapping suggests that transcription initiates at or near the adenine residue which is the first position of the translational initiation triplet (AUG) of STAT. Another open reading frame located just upstream of the STAT gene was detected and contains a region bearing a strong resemblance to DNA-binding domains which are conserved in known DNA-binding proteins. By addition of promoter signals and a synthetic ribosome-binding (Shine-Dalgarno) sequence at an appropriate position upstream of the STAT translational start codon, the STAT gene confers streptothricin resistance on Escherichia coli and Bacillus subtilis. The STAT coding sequence with both the promoter of a B. subtilis cellulase gene and a synthetic Shine-Dalgarno sequence was functionally expressed in Streptomyces lividans, which suggests that the addition of an artificial leader upstream of the translational initiation codon (AUG) does not significantly influence the translation of STAT.

Transformation of Arthrobacter and studies on the transcription of the Arthrobacter ermA gene in Streptomyces lividans and Escherichia coli

We report the development of a plasmid-mediated transformation system for Arthrobacter sp. NRRLB3381, using the Streptomyces cloning vector pIJ702. Our procedure gives a transformation frequency of 10(3)/micrograms of plasmid DNA. In addition we have explored the expression of the Arthrobacter ermA gene in Streptomyces lividans and Escherichia coli, and shown that the ermA promoter is recognized in S. lividans not E. coli. The relationship between Arthrobacter, Streptomyces and E. coli promoters is discussed.

Antimicrobial resistance of Staphylococcus aureus: genetic basis

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Molecular cloning and characterization of the Streptomyces hygroscopicus alpha-amylase gene

We have isolated and sequenced a gene (amy) coding for alpha-amylase (EC 3.2.1.1.) from the Streptomyces hygroscopicus genome (H. Hidaka, Y. Koaze, K. Yoshida, T. Niwa, T. Shomura, and T. Niida, Die Stärke 26:413-416, 1974). Amylase was purified to obtain amino acid sequence information which was used to synthesize oligonucleotide probes. amy-containing Escherichia coli cosmids identified by hybridization did not express amylase activity. Subcloning experiments indicated that amy could be expressed from the lac promoter in E. coli or from its own promoter in S. lividans. The amy nucleotide sequence indicated that it coded for a protein of 52 kilodaltons (478 amino acids). Secreted alpha-amylase contained amino- and carboxy-terminal as well as internal amino acid sequences which were consistent with the nucleotide sequence. The 30-residue leader sequence showed similarities to those found in other procaryotes. The DNA sequence 5' to the amy structural gene contained a sequence complementary to the 3'-terminal sequence of 16S rRNA of S. lividans (M. J. Bibb and S. N. Cohen, Mol. Gen. Genet. 187:265-277, 1982). The transcriptional start points of amy were determined by mung bean nuclease mapping, but the promoter of amy was not similar to the consensus sequence found in other procaryotes.

Extrachromosomal systems and gene transmission in anaerobic bacteria

Obligately anaerobic bacteria are important in terms of their role as medical pathogens as well as their degradative capacities in a variety of natural ecosystems. Two major anaerobic genera, Bacteroides and Clostridium, are examined in this review. Plasmid elements in both genera are reviewed within the context of conjugal transfer and drug resistance. Genetic systems that facilitate the study of these anaerobic bacteria have emerged during the past several years. In large part, these developments have been linked to work centered on extrachromosomal genetic systems in these organisms. Conjugal transfer of antibiotic resistance has been a central focus in this regard. Transposable genetic elements in the Bacteroides are discussed and the evolution and spread of resistance to lincosamide antibiotics are considered at the molecular level. Recombinant DNA systems that employ shuttle vectors which are mobilized by conjugative plasmids have been developed for use in Bacteroides and Clostridium. The application of transmission and recombinant DNA genetic systems to study these anaerobes is under way and is likely to lead to an increased understanding of this important group of procaryotes.

Expression of the macrolide-lincosamide-streptogramin-B-resistance methylase gene, ermE, from Streptomyces erythraeus in Escherichia coli results in N6-monomethylation and N6,N6-dimethylation of ribosomal RNA

The ermE gene was cloned from Streptomyces erythraeus into Escherichia coli on a series of plasmids. When transcribed from the lac promoter, ermE conferred high-level resistance to erythromycin and other macrolide-lincosamide-streptogramin-B (MLS) antibiotics. A methylase activity capable of N6-mono- and N6,N6-dimethylation of adenine residues in E. coli rRNA was detected in extracts of MLS-resistant cells. In addition, rRNA extracted from MLS-resistant E. coli contained N6-mono- and N6,N6-dimethylated adenine residues.

Cloning and analysis of ermG, a new macrolide-lincosamide-streptogramin B resistance element from Bacillus sphaericus

To analyze the regulation of a newly discovered macrolide-lincosamide-streptogramin B resistance element (ermG) found in a soil isolate of Bacillus sphaericus, we cloned this determinant and obtained its DNA sequence. Minicell analysis revealed that ermG specifies a 29,000-dalton protein, the synthesis of which is induced by erythromycin. S1 nuclease mapping was used to identify the transcriptional start site. These experiments demonstrated the presence on the ermG mRNA of a 197 to 198-base leader. Within the leader are two small open reading frames (ORFs) capable of encoding 11- and 19-amino-acid peptides. Each ORF is preceded by a suitably spaced Shine-Dalgarno sequence. The ermG protein is encoded by a large ORF that encodes a 244-amino-acid protein, in agreement with the minicell results. This protein and the 19-amino-acid peptide are highly homologous to the equivalent products of ermC and ermA. We conclude, on the basis of this homology, that ermG encodes an rRNA transmethylase. The leader of ermG can be folded into a structure that sequesters the Shine-Dalgarno sequence and start codon for the large ORF (SD3). On the basis of these data and on the observed greater responsiveness of the ermG system than of the ermC system to low concentrations of erythromycin, we propose a model for the regulation of this gene in which the stalling of a ribosome under the influence of an inducer, while reading either peptide, suffices to uncover SD3 and allow translation of the rRNA transmethylase. The evolution of ermG is discussed.

Cloning and nucleotide sequence of a carbomycin-resistance gene from Streptomyces thermotolerans

Two plasmids (pOJ158 and pOJ159) containing DNA fragments from the carbomycin(Cb)-producing strain Streptomyces thermotolerans were identified in Streptomyces griseofuscus based on their ability to confer resistance to Cb. The Cb-resistance determinants on pOJ158 and pOJ159 were designated carA and carB, respectively. In S. griseofuscus, pOJ159 also confers resistance to spiramycin, rosaramicin, lincomycin, and vernamycin B, but not to tylosin; in Streptomyces lividans, pOJ159 additionally confers resistance to erythromycin and oleandomycin. The carB gene was localized on pOJ159 to a 1.25-kb region whose nucleotide sequence was determined. The sequence has a G + C content of 68% and contains the coding sequence for carB and portions of the 5' and 3' untranslated regions. A comparison of the amino acid sequence of the protein encoded by carB (as deduced from the nucleotide sequence) with the deduced amino acid sequence of the RNA methylase from Streptomyces erythraeus (encoded by ermE) revealed extensive homology, suggesting that carB also encodes an RNA methylase. The region 5' to the coding sequence does not contain a small ORF or regions of complementarity that are commonly associated with translationally regulated macrolide-lincosamide-streptogramin B resistance genes. The 3' untranslated region contains an inverted repeat sequence that potentially can form a stable RNA stem-loop structure with a calculated delta G of -70 kcal.

Complete nucleotide sequence and transcription of ermF, a macrolide-lincosamide-streptogramin B resistance determinant from Bacteroides fragilis

DNA sequence analysis of a portion of an EcoRI fragment of the Bacteroides fragilis R plasmid pBF4 has allowed us to identify the macrolide-lincosamide-streptogramin B resistance (MLSr) gene, ermF. ermF had a relative moles percent G + C of 32, was 798 base pairs in length, and encoded a protein of approximately 30,360 daltons. Comparison between the deduced amino acid sequence of ermF and six other erm genes from gram-positive bacteria revealed striking homologies among all of these determinants, suggesting a common origin. Based on these and other data, we believe that ermF codes for an rRNA methylase. Analysis of the nucleotide sequences upstream and downstream from the ermF gene revealed the presence of directly repeated sequences, now identified as two copies of the insertion element IS4351. One of these insertion elements was only 26 base pairs from the start codon of ermF and contained the transcriptional start signal for this gene as judged by S1 nuclease mapping experiments. Additional sequence analysis of the 26 base pairs separating ermF and IS4351 disclosed strong similarities between this region and the upstream regulatory control sequences of ermC and ermA (determinants of staphylococcal origin). These results suggested that ermF was not of Bacteroides origin and are discussed in terms of the evolution of ermF and the expression of drug resistance in heterologous hosts.

Cloning and analysis of the promoter region of the erythromycin resistance gene (ermE) of Streptomyces erythraeus

A DNA fragment containing the coding and regulatory sequences of the erythromycin (Er) resistance (ermE) gene of the Er produces Streptomyces erythraeus was cloned in Streptomyces lividans using the plasmid vector pIJ61. The approximate location and orientation of ermE were deduced from studies of its expression after subcloning in Escherichia coli. Sequences responsible for transcription of ermE in Streptomyces were studied by nucleotide (nt) sequencing, high resolution S1 and exonuclease VII mapping, in vitro transcription and in vivo promoter-probing. Tandemly arranged promoters of typical prokaryotic appearance initiate transcription of the coding region of ermE; a promoter of similar sequence was identified that initiates transcription of a likely coding region running in the opposite direction to ermE. It is suggested that these sites represent a class of vegetatively expressed Streptomyces promoter that is utilised by a form of RNA polymerase holoenzyme that also recognizes typical promoters of other bacterial genera.