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A Chopin

Publications and source records attributed to A Chopin.

At least 19 recordsLinked to original sources
PubMed2001

Analysis of six prophages in Lactococcus lactis IL1403: different genetic structure of temperate and virulent phage populations.

We report the genetic organisation of six prophages present in the genome of Lactococcus lactis IL1403. The three larger prophages (36-42 kb), belong to the already described P335 group of temperate phages, whereas the three smaller ones (13-15 kb) are most probably satellites relying on helper phage(s) for multiplication. These data give a new insight into the genetic structure of lactococcal phage populations. P335 temperate phages have variable genomes, sharing homology over only 10-33% of their length. In contrast, virulent phages have highly similar genomes sharing homology over >90% of their length. Further analysis of genetic structure in all known groups of phages active on other bacterial hosts such as Escherichia coli, Bacillus subtilis, MYCOBACTERIUM: and Streptococcus thermophilus confirmed the existence of two types of genetic structure related to the phage way of life. This might reflect different intensities of horizontal DNA exchange: low among purely virulent phages and high among temperate phages and their lytic homologues. We suggest that the constraints on genetic exchange among purely virulent phages reflect their optimal genetic organisation, adapted to a more specialised and extreme form of parasitism than temperate/lytic phages.

Bacteriophages↗
PubMed1998

Molecular diversity and relationship within Lactococcus lactis, as revealed by randomly amplified polymorphic DNA (RAPD).

Lactococcus lactis strains are widely used in industrial dairy fermentations. Conventional phenotypic tests have been used for years to classify members of this species into two subspecies, lactis and cremoris, and play a key role in the choice of strains to be used in particular cheese fermentations. DNA hybridisation techniques have also been used for strain classification, giving rise to two genome homology groups. However, results showed discrepancies between the two methods of classification. We applied the randomly amplified polymorphic DNA fingerprinting (RAPD) technique to resolve previous contradictions in lactococcal classifications. Unlike usual RAPD methods, we use three primers to classify 113 strains and integrate the resulting information by a digitised programme used for this purpose. Our analysis revealed three major RAPD groups, designated G1, G2 and G3. G1 and G3 contain strains of the lactis subspecies, and G2 contains strains of the cremoris subspecies, as previously defined by phenotypic characteristics. Moreover, group G1 corresponds to one genome homology group, and groups G2 and G3 correspond to the second one. The taxonomic structure within L. lactis is therefore unusual: two distinct genetic groups of strains show indistinguishable phenotypes, while conversely, two phenotypically distinct groups are genetically homologous. We hypothesize that a subfamily of the subsp. lactis group gave rise to the cremoris subspecies.

DNA Fingerprinting↗
PubMed1998

tRNATrp as a key element of antitermination in the Lactococcus lactis trp operon.

The expression of the trp operon of Lactococcus lactis is regulated in response to tryptophan availability by a mechanism of transcription antitermination. We present evidence in support of a previously described model involving tRNATrp as a key element in the sensing of tryptophan levels and the realization of the regulatory response to tryptophan limitation. In agreement with this model, two sites of presumed direct interaction between the trp leader transcript and tRNATrp are found to be of crucial importance for efficient antitermination. These correspond to the specifier codon, which presumably interacts with the anticodon in the tRNA, and a sequence complementary to, and presumably interacting with, the acceptor stem of the tRNA. Through these interactions, uncharged tRNATrp is believed to stabilize an antiterminator conformation of the trp leader transcript, thus allowing transcription and expression of the structural genes of the operon. For the first time, we present direct evidence that it is the ratio of uncharged to charged tRNA that is important for the regulation of antitermination, rather than the absolute amount of uncharged tRNA. In addition, our results indicate that the codon-anticodon interaction, although contributing largely to the efficiency of the regulatory response, is not strictly indispensable, which suggests the existence of additional interactions between mRNA and tRNA. Finally, we describe a possible additional level of regulation, superimposed and dependent on tRNA-mediated anti-termination control, that is based on the processing of the trp leader transcript. Together with the regulation mechanisms described earlier for the Escherichia coli and Bacillus subtilis trp operons, this constitutes the third different mechanism of transcript elongation control found to be involved in the regulation of an operon of which the structural genes are highly conserved.

Artificial Gene Fusion↗
PubMed1998

Multiple transcriptional control of the Lactococcus lactis trp operon.

The Lactococcus lactis trpEGDCFBA operon is preceded by a noncoding leader region. Transcriptional studies of the trp operon revealed three transcripts with respective sizes of 8 kb (encompassing the entire operon), 290 bases, and 160 bases (corresponding to parts of the leader region). These transcripts most likely result from initiation at the unique Ptrp promoter, transcription termination at either T1 (upstream of the trp operon) or T2 (downstream of the trp operon), and/or processing. Three parameters were shown to differentially affect the amount of these transcripts: (i) following tryptophan depletion, the amount of the 8-kb transcript increases 300- to 500-fold; (ii) depletion in any amino acid increased transcription initiation about fourfold; and (iii) upon entry into stationary phase the amount of the 8-kb transcript decreases abruptly. The tryptophan-dependent transcription control is exerted through transcription antitermination.

Base Sequence↗
PubMed1994

Biochemical and genetic characterization of PepF, an oligopeptidase from Lactococcus lactis.

Lactococcus lactis possesses a complex proteolytic system which is essential for its growth in milk. We characterized one of the peptidases of this system, oligopeptidase PepF, together with its structural gene. PepF hydrolyzed peptides containing between 7 and 17 amino acids with a rather wide specificity. It was purified to homogeneity. The N-terminal sequences of PepF and of peptides resulting from tryptic digestion of PepF were determined and used to design degenerate oligonucleotides which served to amplify a DNA fragment internal to pepF. This fragment was used as a probe to screen a lactococcal genomic library in Escherichia coli and to clone the entire gene pepF. The gene coded for a 70 kDa protein and was located on a 55-kilobase lactose-protease plasmid. A motif His-Glu-X-X-His, characteristic of metallopeptidases was evidenced. Two regions of PepF were found similar, first to a stretch of 43 amino acids around the zinc-binding site of several other peptidases, second to a stretch of 33 amino acids well conserved among creatine and arginine kinases. Preliminary results suggest the presence of a second copy of pepF.

Amino Acid Sequence↗
PubMed1994

BglR protein, which belongs to the BglG family of transcriptional antiterminators, is involved in beta-glucoside utilization in Lactococcus lactis.

A fragment of the Lactococcus lactis chromosome containing an open reading frame of 265 codons, denoted bglR, has been characterized. The polypeptide encoded by bglR shares 36 to 30% sequence identity with a family of regulatory proteins including ArbG from Erwinia chrysanthemi, BglG from Escherichia coli, and SacT and SacY from Bacillus subtilis. These regulatory proteins are involved in positive control of the utilization of different sugars by transcription antitermination. For some of these regulatory proteins it has been demonstrated that antitermination is exerted by binding to a conserved RNA sequence, partially overlapping the transcription terminator and thus preventing transcription termination. Upstream of bglR, we identified a transcription terminator whose 5' end was overlapped by a 32-bp sequence, highly homologous to the RNA-binding site that is conserved in other regulatory systems. Constitutive expression of bglR in E. coli increased the expression of a bglG::lacZ transcriptional fusion. The fact that that the expression of BglG is autoregulated in E. coli suggests that BglG and BglR are functionally equivalent. In L. lactis, we observed that (i) the expression of a bglR::lacZ fusion is increased by beta-glucoside sugars, (ii) disruption of bglR impairs growth on some beta-glucosides, and (iii) the expression of bglR is positively autoregulated. Because of these structural and functional similarities between BglR and the transcription antiterminators of the BglG family, we propose that BglR may be the lactococcal counterpart of the E. coli BglG regulator of beta-glucoside utilization.

Amino Acid Sequence↗
PubMed1993

Organization and regulation of genes for amino acid biosynthesis in lactic acid bacteria.

The recent description of large clusters of biosynthetic genes in the chromosome of Lactococcus lactis and, to a lesser extent, of Lactobacillus, has brought some information on gene organization and control of gene expression in these organisms. The genes involved in a given amino acid biosynthetic pathway are clustered at a single chromosomal location and form an operon. Additional genes which are not required for the biosynthesis are present within some operons. Genetic signals are, in general, similar to those found in other prokaryotes. Several systems controlling gene expression have been identified and transcription attenuation seems frequent. Among the attenuation mechanisms identified, one resembles that controlling amino acid biosynthesis in many bacteria by ribosome stalling at codons corresponding to limiting amino acid. The others are different and might be related to a new class of attenuation mechanism. Preliminary evidence for a new type of regulatory mechanism, involving a metabolic shunt, is also reviewed.

Amino Acids↗
PubMed1993

Cloning and sequencing of pepC, a cysteine aminopeptidase gene from Lactococcus lactis subsp. cremoris AM2.

A gene coding for an aminopeptidase (PepC) from Lactococcus lactis subsp. cremoris AM2 was cloned by complementation of an Escherichia coli mutant lacking aminopeptidase activity. The nucleotide sequence was determined. A portion of the predicted amino acid sequence of PepC (436 amino acids) showed strong homology to the active site of cysteine proteases. No signal sequence was found, indicating an intracellular location of the enzyme.

Amino Acid Sequence↗
PubMed1992

Tryptophan biosynthesis genes in Lactococcus lactis subsp. lactis.

The Lactococcus lactis chromosomal region containing the seven structural genes required for tryptophan biosynthesis was characterized by cloning and sequencing. All of the trp genes were identified by the homology of their products with known Trp proteins from other organisms. The identification was confirmed for five genes by their ability to complement trp mutations in Escherichia coli. The seven structural genes are present in the order trpEGDCFBA and span a 7,968-bp segment. Each gene is preceded by a putative ribosome binding site complementary to the 3' end of the L. lactis 16S rRNA. Three pairs of genes (trpG-trpD, trpC-trpF, and trpB-trpA) overlap, and there is intercistronic spacing of 124, 46, and 585 bp between the trpE-trpG, trpD-trpC, and trpF-trpB gene pairs, respectively. No gene fusion was found. Upstream of the trp genes, a 457-bp noncoding DNA segment contains several regions fitting the consensus for gram-positive promoters and one region strongly resembling a transcription terminator. However, it seems unlikely that an attenuation mechanism similar to the one found in E. coli regulates tryptophan biosynthesis in L. lactis, since no potential leader peptide was detected. We propose that a mechanisms resembling that described in Bacillus spp. can regulate trp genes expression in L. lactis.

Amino Acid Sequence↗
PubMed1991

[Enteral feeding. Principles and techniques, nutritive solutions].

A great number of nutritional solutions can be found owing to the technical progress of enteral nutrition and the diversity of available nutritive solutions. In this paper are described the various materials, their advantages and disadvantages together with the available nutritive solutions. The interests of new methods of gastrostomy by endoscopy and the progress due to the use of nutritive pumps are pointed out. Physicians can now choose the type of feeding adapted to specific nutrients requirements of the patients. They can also vary it in relation to its tolerance and the evolution of nutritional situation. Practice of enteral nutrition needs a very accurate knowledge of material, nutritive solutions and technical uses. They also have to be in agreement with the strict obligations of food hygiene.

Enteral Nutrition↗
PubMed1991

Cloning and DNA sequence analysis of an X-prolyl dipeptidyl aminopeptidase gene from Lactococcus lactis subsp. lactis NCDO 763.

Lactococcus lactis subsp. lactis NCDO 763 (also designated ML3) possesses an X-prolyl dipeptidyl aminopeptidase (X-PDAP; EC 3.4.14.5). X-PDAP mutants were selected by an enzymatic plate assay on the basis of their inability to hydrolyze an L-phenylalanyl-L-proline-beta-naphthylamide substrate. A DNA bank from L. lactis subsp. lactis NCDO 763 was constructed in one of these X-PDAP mutants, and one clone in which the original X-PDAP phenotype was restored was detected by the enzymatic plate assay. The X-PDAP gene, designated pepXP, was further subcloned and sequenced. It codes for a protein containing 763 residues. Comparison of the amino-terminal sequence of the X-PDAP enzyme with the amino acid sequence deduced from the pepXP gene indicated that the enzyme is not subjected to posttranslational modification or exported via processing of a signal peptide. The pepXP gene from L. lactis subsp. lactis NCDO 763 in more than 99% homologous to the pepXP gene from L. lactis subsp. cremoris P8-2-47 described elsewhere (B. Mayo, J. Kok, K. Venema, W. Bockelmann, M. Teuber, H. Reinke, and G. Venema, Appl. Environ. Microbiol. 57:38-44, 1991) and is also conserved in other lactococcal strains.

Amino Acid Sequence↗
PubMed1991

Phage abortive infection mechanism from Lactococcus lactis subsp. lactis, expression of which is mediated by an Iso-ISS1 element.

A 5-kb DNA fragment conferring a phage abortive infection phenotype (Abi+) has been cloned from Lactococcus lactis subsp. lactis IL416. The Abi+ determinant was subcloned on a 2-kb fragment which carried an Iso-ISS1 element and an open reading frame of 753 bp designated ORFX. Deletion within ORFX entailed the loss of the Abi+ phenotype, establishing that ORFX is the structural abi-416 gene. The expression of abi-416 was shown to be mediated by the Iso-ISS1 element, which contains a sequence fitting the consensus sequence for gram-positive promoters.

Amino Acid Sequence↗
PubMed1989

Conjugal transfer of plasmid pIP501 from Lactococcus lactis to Lactobacillus delbrückii subsp. bulgaricus and Lactobacillus helveticus.

Plasmid pIP501 was transferred by conjugation from Lactococcus lactis to Lactobacillus delbrückii subsp. bulgaricus and Lactobacillus helveticus. Only Lb. delbrückii subsp. bulgaricus transconjugants could act as a donor in crosses with Lc. lactis. No Lactobacillus transconjugants were detected after inter- or intra-species Lactobacillus crosses. Plasmid pIP501 has undergone no detectable deletion or rearrangement during transfer from Lc. lactis to Lactobacillus strains.

Conjugation, Genetic↗
PubMed1989

Insertion and amplification of foreign genes in the Lactococcus lactis subsp. lactis chromosome.

The plasmid pE194 is unable to replicate in Lactococcus lactis subsp. lactis (formerly Streptococcus lactis). When linked to resident bacteriophage sequences, pE194 was able to integrate into the L. lactis subsp. lactis chromosome either by Campbell-like recombination or by double crossing over with deletion. Integration occurred into the DNA of the prophage and prevented its multiplication. When a selective pressure was applied to an integrant in which pE194 was flanked by two direct repeats of prophage fragment, amplification of pE194 and the prophage fragment was observed. The pE194 copy number was assessed at six to nine, and amplification was stable upon growth under nonselective conditions.

Bacteriophages↗
PubMed1988

Construction of a vector plasmid family and its use for molecular cloning in Streptococcus lactis.

Cloning vector plasmids have been constructed on the basis of the broad host range plasmid pAM beta 1 and used for the cloning of a nisin resistance determinant in Streptococcus lactis. They incorporate several desirable features for gene cloning in S. lactis and other transformable Gram-positive bacteria. They carry an easily selectable erythromycin resistance marker, are present at low (6-9) or high (45-85) copy number in S. lactis and possess a convenient polyrestriction site sequence. A significant advantage of these plasmids is their capability to carry and stably maintain very large cloned DNA fragments (up to 30 kilobases).

Cloning, Molecular↗
PubMed1986

Cloning in Streptococcus lactis of plasmid-mediated UV resistance and effect on prophage stability.

Plasmid pIL7 (33 kilobases) from Streptococcus lactis enhances UV resistance and prophage stability. A 5.4-kilobase pIL7 fragment carrying genes coding for both characters was cloned into S. lactis, using plasmid pHV1301 as the cloning vector. The recombinant plasmid was subsequently transferred to three other S. lactis strains by transformation or protoplast fusion. Cloned genes were expressed in all tested strains.

Bacillus subtilis↗