Expression in Escherichia coli of a staphylococcal gene for resistance to macrolide, lincosamide, and streptogramin type B antibiotics

Triphenylphosphonium Analogs of Short Peptide Related to Bactenecin 7 and Oncocin 112 as Antimicrobial Agents

Antimicrobial peptides (AMPs) have recently attracted attention as promising antibacterial agents capable of acting against resistant bacterial strains. In this work, an approach was applied, consisting of the conjugation of a peptide related to the sequences of bactenecin 7 (Bac7) and oncocin (Onc112) with the alkyl(triphenyl)phosphonium (alkyl-TPP) fragment in order to improve the properties of the AMP and introduce new ones, expand the spectrum of antimicrobial activity, and reduce the inhibitory effect on the eukaryotic translation process. Triphenylphosphonium (TPP) derivatives of a decapeptide RRIRPRPPYL were synthesized. It was comprehensively studied how the modification of the AMP affected the properties of the new compounds. It was shown that while the reduction in the Bac7 length to 10 a.a. residues dramatically decreased the affinity to bacterial ribosomes, the modification of the peptide with alkyl-TPP moieties led to an increase in the affinity. New analogs with structures that combined a decapeptide related to Bac7 and Onc112-Bac(1-10, R/Y)-and TPP attached to the C-terminal amino acid residue via alkylamide linkers, inhibited translation in vitro and were found to be more selective inhibitors of bacterial translation compared with eukaryotic translation than Onc112 and Bac7. The TPP analogs of the decapeptide related to Bac7 and Onc112 suppressed the growth of both Gram-negative bacteria, similar to Onc112 and Bac7, and Gram-positive ones, similar to alkyl-TPP derivatives, and also acted against some resistant laboratory strains. Bac(1-10, R/Y)-C2-TPP, containing a short alkylamide linker between the decapeptide and TPP, was transferred into the E. coli cells via the SbmA transporter protein. TPP derivatives of the decapeptide Bac(1-10, R/Y) containing either a decylamide or ethylamide linker caused B. subtilis membrane depolarization, similar to alkyl-TPP. The Bac(1-10, R/Y)-C2-TPP analog was proven to be non-toxic for mammalian cells using the MTT test.

Conjugates of Desmycosin with Fragments of Antimicrobial Peptide Oncocin: Synthesis, Antibacterial Activity, Interaction with Ribosome

Design and synthesis of conjugates consisting of the macrolide antibiotic desmycosin and fragments of the antibacterial peptide oncocin were performed in attempt to develop new antimicrobial compounds. New compounds were shown to bind to the E. coli 70S ribosomes, to inhibit bacterial protein synthesis in vitro, as well as to suppress bacterial growth. The conjugates of N-terminal hexa- and tripeptide fragments of oncocin and 3,2',4''-triacetyldesmycosin were found to be active against some strains of macrolide-resistant bacteria. By simulating molecular dynamics of the complexes of these compounds with the wild-type bacterial ribosomes and with ribosomes, containing A2059G 23S RNA mutation, the specific structural features of their interactions were revealed.

Induction of erm(C) expression by noninducing antibiotics

Ketolides, which represent the newest macrolide antibiotics, are generally perceived to be noninducers of inducible erm genes. In the study described in this paper we investigated the effects of several macrolide and ketolide compounds on the expression of the inducible erm(C) gene by Escherichia coli cells. Exposure to 14-member-ring macrolide drugs and to azithromycin led to a rapid and pronounced increase in the extent of dimethylation of Erm(C) target residue A2058 in 23S rRNA. When cells were incubated with subinhibitory concentrations of ketolides, the extent of A2058 dimethylation was also increased, albeit to a lower level and with kinetics slower than those observed with macrolides. The induction of erm(C) expression by ketolides was further confirmed by using a reporter construct which allows the colorimetric detection of induction in a disc diffusion assay. Most of the ketolides tested, including the clinically relevant compounds telithromycin and cethromycin, were able to induce the reporter expression, even though the induction occurred within a more narrow range of concentrations compared to the concentration range at which induction was achieved with the inducing macrolide antibiotics. No induction of the reporter expression was observed with 16-member-ring macrolide antibiotics or with a control drug, chloramphenicol. The deletion of three codons of the erm(C) leader peptide eliminated macrolide-dependent induction but left ketolide-dependent induction unchanged. We conclude that ketolides are generally capable of inducing erm genes. The narrow range of ketolide inducing concentrations, coupled with the slow rate of induction and the lower steady-state level of ribosome methylation, may mask this effect in MIC assays.

Presence of erm gene classes in gram-positive bacteria of animal and human origin in Denmark

A classification of the different erm gene classes based on published sequences was performed, and specific primers to detect some of these classes designed. The presence of ermA (Tn554), ermB (class IV) and ermC (class VI) was determined by PCR in a total of 113 enterococcal, 77 streptococcal and 68 staphylococcal erythromycin resistant isolates of animal and human origin. At least one of these genes was detected in 88% of the isolates. Four isolates contained more than one erm gene. ermB dominated among the enterococci (88%) and streptococci (90%) and ermC among staphylococci (75%) with ermA (Tn554) present in some isolates (16%). Variations in the presence of the different genes when comparing staphylococcal isolates of human and animal origin were observed.

Inducible expression of ribosomal clindamycin resistance in Bacteroides vulgatus

The abilities of erythromycin and clindamycin to act as inducers of clindamycin resistance in the strain Bacteroides vulgatus RYC18F6 is evaluated in vivo (efficiency of plating of inhibitory clindamycin concentrations) and in vitro [efficiency of poly(U)-directed polypeptide synthesis by ribosomes]. Uninduced cells failed to grow during the first 72 h, even at a very low clindamycin concentration (0.1 microgram/ml); after induction with erythromycin or clindamycin, cells were able to form colonies at 32 micrograms/ml after 48 h. The in vitro polymerization test with B. vulgatus RYC18F6 ribosomes (S-30 extract) showed that ribosomes from uninduced cells were fully sensitive to the inhibitory effect of clindamycin. Ribosomes obtained from erythromycin- or clindamycin-induced cells presented a reduced sensitivity to clindamycin inhibition. These results show that resistance to clindamycin in B. vulgatus RYC18F6 is an inducible phenomenon involving a ribosomal modification, probably similar to that previously described for gram-positive bacteria.

Identification and cloning of the conjugative transfer region of Staphylococcus aureus plasmid pGO1

The conjugative transfer (tra) genes of a 52-kilobase (kb) staphylococcal plasmid, pGO1, were localized by deletion analysis and transposon insertional inactivation. All transfer-defective (Tra-) deletions and Tn551 or Tn917 transposon insertions occurred within a 14.5-kb BglII fragment. Deletions and insertions outside this fragment all left the plasmid transfer proficient (Tra+). The tra region was found to be flanked by directly repeated DNA sequences, approximately 900 base pairs in length, at either end. Clones containing the 14.5-kb BglII fragment (pGO200) and subclones from this fragment were constructed in Escherichia coli on shuttle plasmids and introduced into Staphylococcus aureus protoplasts. Protoplasts could not be transformed with pGO200E (pGO200 on the staphylococcal replicon, pE194) or subclones containing DNA at one end of the tra fragment unless pGO1 or specific cloned tra DNA fragments were present in the recipient cell. However, once stabilized by sequences present on a second replicon, each tra fragment could be successfully introduced alone into other plasmid-free S. aureus recipients by conjugative mobilization or transduction. In this manner, two clones containing overlapping fragments comprising the entire 14.5-kb BglII fragment were shown to complement each other. The low-frequency transfer resulted in transconjugants containing one clone intact, deletions of that clone, and recombinants of the two clones. The resulting recombinant plasmid (pGO220), which regenerated the tra region intact on a single replicon, transferred at frequencies comparable to those of pGO1. Thus, all the genes necessary and sufficient for conjugative transfer of pGO1 are contained within a 14.5-kb region of DNA.

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.

Constitutive expression of erythromycin resistance mediated by the ermAM determinant of plasmid pAM beta 1 results from deletion of 5' leader peptide sequences

We have sequenced the erythromycin resistance determinant (erm) of the Streptococcus faecalis plasmid pAM beta 1 to investigate its relationship to other known resistance determinants. We show that this determinant is strongly (99%) homologous at the DNA level to that of plasmid pAM77 (Streptococcus sanguis) and of transposon Tn917 (S. faecalis). Moreover, nucleotide sequence comparison with the determinants of pAM77 and Tn917 shows that most of the probable regulatory region is absent, providing an explanation for the constitutive expression of the pAM beta 1 erm determinant.

Prevalence of macrolides-lincosamides-streptogramin B resistance and erm gene classes among clinical strains of staphylococci and streptococci

A total of 332 staphylococcal and 263 streptococcal isolates from three hospital microbiology laboratories were tested with erythromycin, clindamycin, and vernamycin B alpha to determine the prevalence of macrolides-lincosamides-streptogramin B resistance. Constitutive resistance was detected in 28 Staphylococcus aureus isolates (15.5%), 53 coagulase-negative staphylococci (35.1%), and 20 streptococci (7.6%). Inducible resistance was observed in 13 S. aureus isolates (7.2%), 25 coagulase-negative staphylococci (16.6%), and 2 streptococci (0.8%). Eleven coagulase-negative staphylococci (7.3%) exhibited a novel phenotype, namely inducible resistance to erythromycin and vernamycin B alpha but not clindamycin. Among the staphylococci, two variants of the inducible phenotype detected with the agar diffusion assay correlated with the presence of classical ermA or ermC genes, respectively, by dot-blot analysis. The prevalence of the staphylococcal phenotypes were different in the hospitals surveyed, and there was an apparent inverse correlation between the resistance observed and the use of erythromycin in each hospital.

Molecular epidemiology of macrolides-lincosamides-streptogramin B resistance in Staphylococcus aureus and coagulase-negative staphylococci

Macrolides-lincosamides-streptogramin B (MLS) resistance is commonly found in Staphylococcus aureus and coagulase-negative staphylococci (22 and 45%, respectively, among isolates from three New Jersey hospitals). We have examined representative subsets of 107 MLS-resistant isolates for the molecular nature of the resistance determinant, the erm gene, by dot blot and Southern hybridization analysis. All of 35 S. aureus isolates examined and 39 of 42 coagulase-negative isolates examined were found to harbor the ermA or ermC evolutionary variant. Genes of the ermC class occurred exclusively on a small plasmid similar to or indistinguishable from one (pNE131) previously described in S. epidermidis. Genes of the ermA class occurred exclusively in the chromosome, and restriction patterns indicated that they were part of a transposon, Tn554, characteristic of the classical S. aureus ermA strain. Unlike S. aureus ermA strains examined previously, which harbor Tn554 at a single specific (primary) site, four of our S. aureus isolates had second inserts at different chromosomal sites. The majority of our coagulase-negative isolates had two or more inserts, neither of which occurred at the classical primary site and many of which differed from one another in location (as inferred from restriction patterns). Coagulase-negative staphylococci constitute a large reservoir of the ermA and ermC class of determinants, with clear potential for interspecies spread.

Staphylococcal resistance to aminoglycosides before and after introduction of amikacin in two teaching hospitals

A prospective study was conducted to determine the prevalence of aminoglycoside-resistant Staphylococcus aureus and coagulase-negative staphylococci before and after the introduction of amikacin as the sole aminoglycoside used in our burn unit, adult intensive care unit, and neonatal intensive care unit. Pharyngeal or endotracheal cultures, as well as superficial surveillance cultures, were collected weekly during the following four study periods: all units for 4 months before amikacin introduction, all units 4 to 8 months after, all units 12 to 13 months after, and the neonatal intensive care unit 30 months after. A total of 2,613 strains of coagulase-negative staphylococci and 316 strains of S. aureus were obtained from 916 patients. During the course of the study, amikacin-resistant coagulase-negative staphylococci increased from 0 to 22%, colonizing 43% of patients, whereas no amikacin-resistant S. aureus was detected. During the preamikacin survey, 68% of the coagulase-negative staphylococci and 12% of the S. aureus strains were resistant to tobramycin and gentamicin. This resistance did not decrease after amikacin was introduced. Initially, 83% of the aminoglycoside-resistant coagulase-negative staphylococci were resistant to both tobramycin and gentamicin. During the last surveillance this value dropped to 40%, and 48% of the strains had become resistant to all three aminoglycosides. Resistance to aminoglycosides, including amikacin, develops quickly in coagulase-negative staphylococci from clinical areas where these antimicrobial agents are widely used. However, aminoglycoside resistance in S. aureus is much less frequent.

Mapping and cloning of Corynebacterium diphtheriae plasmid pNG2 and characterization of its relatedness to plasmids from skin coryneforms

The relationship of plasmid pNG2, isolated from an erythromycin-resistant strain of Corynebacterium diphtheriae, to plasmids isolated from skin coryneforms was examined. The extent of homology between plasmids from erythromycin-resistant and -susceptible skin coryneforms and pNG2 varied, but in aggregate homology was observed with all six BstEII fragments of pNG2. The data support the hypothesis that pNG2 originated in skin coryneforms. Intact plasmid pNG2 and some of its restriction fragments were cloned into Escherichia coli JM109. The erythromycin resistance phenotype was expressed in clones carrying intact pNG2 as well as in some of its fragments and appeared to depend on a C. diphtheriae promoter for expression. A 2.5-megadalton EcoRI fragment, the smallest expressing resistance, contained the 1.2-megadalton region of pNG2 which is deleted when the erythromycin-resistant strain of C. diphtheriae reverts spontaneously to the susceptible state.

New plasmid expression vectors for Bacillus subtilis

The construction of new cloning vectors for Bacillus subtilis is described. They are derived from the in vitro joining of parts of pE194 and pUB110 DNAs. Their common feature is to present a cloning site immediately after the promoter and ribosome binding site of the erythromycin resistance gene, allowing the insertion and expression of either sticky or blunt ended DNA fragments coding for any heterologous gene. The cloning and expression of Escherichia coli beta-lactamase and EcoRI methylase are given as examples. The enzymes are efficiently synthesized by B. subtilis cells.

Ribosomal RNA methylation in Staphylococcus aureus and Escherichia coli: effect of the "MLS" (erythromycin resistance) methylase

Classical acquired resistance to erythromycin in Staphylococcus aureus ("MLS," or macrolide-lincosamide-streptogramin, resistance) was shown by Weisblum and colleagues to be a direct consequence of the conversion of one or more adenosine residues of 23S rRNA, within the subsequence(s) GA3G, to N6-dimethyladenosine (m62A). The methylation reaction is effected by a class of methylase, whose genes are typically plasmid- or transposon-associated, and whose synthesis is inducible by erythromycin. Using a recently obtained clinical MLS isolate of S. aureus, we have further defined the methylation locus as YGG X m62A X AAGAC; and have shown that this subsequence occurs once in the 23S RNA and that it is essentially completely methylated in all copies of 23S RNA that accumulate in induced cultures. Similar findings were obtained with laboratory S. aureus strains containing two well-characterized evolutionary variants (ermB, ermC) of MLS methylase genes. Analyses of a strain of E. coli containing the ermC gene indicated that the specificity of the methylase gene was unchanged, but that its expression was muted. Even after prolonged periods of induction, the strain manifested only partial resistance to erythromycin, and only about one-third of the copies of the MLS subsequence were methylated in such "induced" cultures. Since the E. coli 23S RNA sequence is known in its entirety, localization of the MLS subsequence is in this case unambiguous; as inferred by homology arguments applied earlier to the S. aureus data, the subsequence is in a highly conserved region of 23S RNA considered to contribute to the peptidyl transferase center of the ribosome.

Construction and application of a promoter-probe plasmid that allows chromogenic identification in Streptomyces lividans

We cloned a Streptomyces coelicolor A3(2) DNA fragment which directed synthesis of a brown pigment, presumably a shunt product in the actinorhodin biosynthetic pathway, on the plasmid vector pIJ41 in Streptomyces lividans. The pigment production was observed only when the DNA fragment was inserted downstream from a functional promoter sequence. By subcloning the fragment together with in vitro manipulation, a promoter-probe plasmid vector (pARC1) with a unique BamHI cloning site was constructed that allows chromogenic identification of transcriptional control signals in Streptomyces lividans based on the expression of the cloned pigment gene(s). The Escherichia coli tac (trp-lac hybrid) promoter, consisting of 92 base pairs and a promoter region including the leader sequence of erythromycin resistance gene (ermC) on staphylococcal plasmid pE194, when ligated in the correct orientation in the BamHI site of pARC1, promoted expression of the cloned pigment gene(s) in Streptomyces lividans, whereas the Saccharomyces cerevisiae GAL7 promoter did not. In the case of the ermC, induction of the pigment production by the addition of either erythromycin or lincomycin, but not virginiamycin, was observed. The system was also shown to be useful and convenient in isolating transcriptional control signals of Streptomyces chromosomal DNA and estimating their activities.

Expression in Escherichia coli of streptococcal plasmid-determined erythromycin resistance directed by the cat gene promoter of pACYC 184

The streptococcal erythromycin resistance (Emr) plasmid pSM7 (6.4 kb) and the E. coli vector pACYC184 (4.0 kb) were fused at their single EcoRI sites to form the bifunctional chimeric plasmid pSM7184 (10.4 kb) in which the Emr determinant was placed under control of the chloramphenicol acetyl transferase (cat) promoter of pACYC184. In the sense orientation (orientation I) of pSM7, the cat promoter directed expression of Emr in the E. coli host strains 294 and DB11 more efficiently than did the indigenous transcription signals of pSM7, which were functional in the opposite orientation II. In Streptococcus sanguis (Challis), the level of Emr was independent of the orientation of pSM7 in pACYC184, showing that the cat promoter was not recognized in the gram-positive host. The growth of E. coli (pSM7184I) in a defined medium containing glycerol as carbon source, or containing glucose plus extraneous cyclic 3'-5' adenosine monophosphate (cAMP) led to an Emr level which was 15-30 times higher than that of cultures grown on glucose. These results showed that under control of the cat promoter, Emr is subject to cAMP-mediated catabolite repression and provided conclusive evidence that the enhancement of Emr expression in E. coli carrying pSM7184I is controlled at the transcriptional level. Besides enabling us to determine the orientation of transcription of the Emr gene in pSM7 and related vectors, this work also made available new bifunctional cloning vehicles able to replicate in both E. coli and S. sanguis.

Construction of plasmid cloning vectors for lactic streptococci which also replicate in Bacillus subtilis and Escherichia coli

The cryptic Streptococcus cremoris Wg2 plasmid pWV01 (1.5 megadaltons) was genetically marked with the chloramphenicol resistance (Cmr) gene from pC194. The recombinant plasmid (pGK1, 2.4 megadaltons) replicated and expressed Cmr in Bacillus subtilis. From this plasmid an insertion-inactivation vector was constructed by inserting the erythromycin resistance (Emr) gene from pE194 cop-6. This plasmid (pGK12, 2.9 megadaltons) contained a unique BclI site in the Emr gene and unique ClaI and HpaII sites outside both resistance genes. It was stably maintained in B. subtilis at a copy number of approximately 5. pGK12 also transformed Escherichia coli competent cells to Cmr and Emr. The copy number in E. coli was about 60. Moreover, pGK12 transformed protoplasts of Streptococcus lactis. In this host both resistance genes are expressed. pGK12 is stably maintained in S. lactis at a copy number of 3.

Regulation of a macrolide resistance-beta-galactosidase (ermC-lacZ) gene fusion in Escherichia coli

A fusion constructed between the putative attenuator plus the first 219 nucleotides of the ermC (erythromycin resistance) structural gene and a 5' terminally deleted lacZ gene produced a moderate, basal level of beta-galactosidase which was increased by erythromycin addition. Another construction containing an intact ermC gene in addition to the fusion produced lower levels of beta-galactosidase, suggesting that the ermC gene product exerts negative feedback control on expression.

Antibiotic resistance mutations in 16S and 23S ribosomal RNA genes of Escherichia coli

Recombinant DNA and classic genetic procedures were used to map a spectinomycin resistance mutation to a 121 base pair region of a 16S RNA gene and a macrolide-lincosamide-streptogramin type B resistance mutation to a 32 base pair region of a 23S RNA gene. DNA sequence analysis of these regions revealed that spectinomycin resistance results from a C/G to T/A transition at position 1192 of a 16S RNA gene. Resistance to macrolide, lincosamide and streptogramin type B antibiotics results from an A/T to T/A transversion at position 2058 of a 23S RNA gene. The alteration in 16S RNA is in a sequence that can participate in alternate base pairing arrangements that have been proposed to be involved in the translocation process. The alteration in 23S RNA identifies sequences important to peptidyl transfer.

The "erythromycin-resistance" methylated sequence of Staphylococcus aureus ribosomal RNA

We have determined the sequence of an oligonucleotide from the large ribosomal subunit RNA of Staphylococcus aureus whose methylation renders the organism resistant to erythromycin and other antibiotics (the "MLS" phenotype). Analysis of RNase A digests of [3H]methyl-, 32P-labeled RNA yielded the sequence GG . m6(2)A . AAGACp, where m6(2)A is an N6-dimethylated adenosine residue that in sensitive cells is unmethylated. Comparison with homologous sequences recently reported for Saccharomyces cerevesiae mitochondria indicates that an A to G mutation in this latter system mimics dimethylation in St. aureus with regard to functional consequences.

Expression of a cloned Staphylococcus aureus alpha-hemolysin determinant in Bacillus subtilis and Staphylococcus aureus

A DNA sequence encoding Staphylococcus aureus alpha-hemolysin, which had been previously cloned and mapped in Escherichia coli K-12, was introduced into Bacillus subtilis BD170 and several strains of S. aureus by using plasmid vectors, some of which could replicate in all three organisms. The determinant was cloned on a 3.3-kilobase pair DNA fragment into B. subtilis by using the vector plasmid pXZ105 to form the hybrid plasmid pXZ111. B. subtilis cells harboring pXZ111 produced large zones of alpha-hemolysis after 18 h of growth at 37 degrees C on rabbit blood agar plates, and alpha-hemolysin activity was detected in supernatants prepared from growing cultures of this strain. The alpha-hemolysin was apparently secreted across the B. subtilis cell envelope. Polypeptides of molecular weights 34,000 and 33,000 were precipitated with anti-alpha-hemolysin serum from lysates prepared from BD170 cells harboring pXZ111. A hybrid replicon which could replicate in both E. coli and S. aureus was constructed in E. coli by ligating a HindIII fragment encoding the replication functions and chloramphenicol resistance genes of S. aureus plasmid pCW59 to the pBR322 alpha-hemolysin hybrid plasmid pDU1150. The DNA of this plasmid, pDU1212, was prepared in E. coli and used to transform protoplasts prepared from a non-alpha-hemolytic, nonrestricting strain of S. aureus RN4220. Some of the transformants contained plasmids which had suffered extensive deletions. Some plasmids, however, were transformed intact into RN4220. Such plasmids were subsequently maintained in a stable manner. pDU1212 DNA was prepared from RN4220 and transformed into alpha-hemolytic S. aureus 8325-4 and two mutant derivatives defective in alpha-hemolysin synthesis. All three strains expressed alpha-hemolysin when harboring pDU1212.

A complex attenuator regulates inducible resistance to macrolides, lincosamides, and streptogramin type B antibiotics in Streptococcus sanguis

Macrolide-lincosamide-streptogramin B resistance specified by Streptococcus sanguis plasmid pAM77 involves an adenine methylase, whose synthesis, demonstrable both phenotypically and by analysis of methionine-labeled proteins made in Bacillus subtilis minicells, is inducible by erythromycin, lincomycin, and streptogramin type B antibiotics. Localization of the methylase structural gene, including its control region in DNA fragments obtained with restriction endonucleases, has been deduced from DNA blot experiments with characterized target and probe DNAs from other streptococci, combined with DNA sequence analysis and comparison of the putative streptococcal methylase sequence with that of a cognate methylase in staphylococcal plasmid pE194. The streptococcal methylase migrates electrophoretically in polyacrylamide gels with the mobility of a 29,000-dalton protein. The sequence organization of the putative streptococcal methylase mRNA leader sequence partially resembles its staphylococcal counterpart and can support a similar mechanism of secondary structure rearrangement leading to methylase synthesis. The deduced 5' leader sequence preceding the pAM77 methylase structural gene sequence comprises approximately 155 nucleotides within which one can identify a putative control peptide 36 amino acid residues in length (in contrast to 19 in the pE194 peptide) and at least 14 possible classes of overlapping inverted complementary repeat sequences (in contrast to 3 in the pE194 control region), one of which can sequester the sequence AGGAG 7 nucleotides upstream from the putative (methionine) start codon of the streptococcal methylase. Comparison of the pAM77 and pE194 methylase amino acid sequences and their respective nucleotide sequences shows 51% conservation of amino acid residues (124 of 244) and 59% conservation of nucleotide residues (433 of 738), which suggests a common origin for the two methylase structural gene sequences. Differences in mRNA base composition associated with conserved amino acid residues occur mostly in the third nucleotide ("wobble") position of codons and may reflect adaptation of methylase genes to optimal expression in host cells with differing codon use patterns.