Showing papers on "Lambda phage published in 1999"

Escherichia coli Mutants Lacking All Possible Combinations of Eight Penicillin Binding Proteins: Viability, Characteristics, and Implications for Peptidoglycan Synthesis

Abstract: The penicillin binding proteins (PBPs) synthesize and remodel peptidoglycan, the structural component of the bacterial cell wall. Much is known about the biochemistry of these proteins, but little is known about their biological roles. To better understand the contributions these proteins make to the physiology of Escherichia coli, we constructed 192 mutants from which eight PBP genes were deleted in every possible combination. The genes encoding PBPs 1a, 1b, 4, 5, 6, and 7, AmpC, and AmpH were cloned, and from each gene an internal coding sequence was removed and replaced with a kanamycin resistance cassette flanked by two res sites from plasmid RP4. Deletion of individual genes was accomplished by transferring each interrupted gene onto the chromosome of E. coli via lambda phage transduction and selecting for kanamycin-resistant recombinants. Afterwards, the kanamycin resistance cassette was removed from each mutant strain by supplying ParA resolvase in trans, yielding a strain in which a long segment of the original PBP gene was deleted and replaced by an 8-bp res site. These kanamycin-sensitive mutants were used as recipients in further rounds of replacement mutagenesis, resulting in a set of strains lacking from one to seven PBPs. In addition, the dacD gene was deleted from two septuple mutants, creating strains lacking eight genes. The only deletion combinations not produced were those lacking both PBPs 1a and 1b because such a combination is lethal. Surprisingly, all other deletion mutants were viable even though, at the extreme, 8 of the 12 known PBPs had been eliminated. Furthermore, when both PBPs 2 and 3 were inactivated by the beta-lactams mecillinam and aztreonam, respectively, several mutants did not lyse but continued to grow as enlarged spheres, so that one mutant synthesized osmotically resistant peptidoglycan when only 2 of 12 PBPs (PBPs 1b and 1c) remained active. These results have important implications for current models of peptidoglycan biosynthesis, for understanding the evolution of the bacterial sacculus, and for interpreting results derived by mutating unknown open reading frames in genome projects. In addition, members of the set of PBP mutants will provide excellent starting points for answering fundamental questions about other aspects of cell wall metabolism.

Family values in the age of genomics: comparative analyses of temperate bacteriophage HK022.

Abstract: ▪ Abstract HK022 is a temperate coliphage related to phage λ. Its chromosome has been completely sequenced, and several aspects of its life cycle have been intensively studied. In the overall arrangement, expression, and function of most of its genes, HK022 broadly resembles λ and other members of the λ family. Upon closer view, significant differences emerge. The differences reveal alternative strategies used by related phages to cope with similar problems and illuminate previously unknown regulatory and structural motifs. HK022 prophages protect lysogens from superinfection by producing a sequence-specific RNA binding protein that prematurely terminates nascent transcripts of infecting phage. It uses a novel RNA-based mechanism to antiterminate its own early transcription. The HK022 protein shell is strengthened by a complex pattern of covalent subunit interlinking to form a unitary structure that resembles chainmail armor. Its integrase and repressor proteins are similar to those of λ, but the differen...

Cloning and expression in Escherichia coli of an azoreductase gene from Clostridium perfringens and comparison with azoreductase genes from other bacteria.

Abstract: A genomic library of Clostridium perfringens ATCC 3626 was constructed in phage lambda gt11 and screened with an antibody against the C. perfringens azoreductase, which catalyzes the reduction of azo dyes to aromatic amines. A positive recombinant phage, containing a 3.8 kb DNA fragment insert was selected and purified. Lytic and lysogenic Escherichia coli cultures infected with the recombinant phage had higher azoreductase activity than cultures infected only with the vector lambda gt11. The 3.8 kb DNA fragment was amplified by PCR and found to hybridize with one band from C. perfringens DNA digested with EcoR1, indicating the presence of a single copy of the azoreductase gene. The fragment also hybridized with DNA from other azoreductase-producing Clostridium species, a Eubacterium sp., Enterobacter cloacae, Citrobacter amalonaticus and E. coli, but not with DNA from some other species of anaerobic bacteria capable of reducing azo dyes. The data indicate that the sequence of the azoreducatse gene of C. perfringens is conserved in some anaerobes and facultative anaerobes, but not in others, and that different types of azoreductase genes must be found in other anaerobic bacteria.

Roles of RuvC and RecG in phage lambda red-mediated recombination.

Abstract: The recombination properties of Escherichia coli strains expressing the red genes of bacteriophage lambda and lacking recBCD function either by mutation or by expression of lambda gam were examined. The substrates for recombination were nonreplicating lambda chromosomes, introduced by infection; Red-mediated recombination was initiated by a double-strand break created by the action of a restriction endonuclease in the infected cell. In one type of experiment, two phages marked with restriction site polymorphisms were crossed. Efficient formation of recombinant DNA molecules was observed in ruvC+ recG+, ruvC recG+, ruvC+ recG, and ruvC recG hosts. In a second type of experiment, a 1-kb nonhomology was inserted between the double-strand break and the donor chromosome's restriction site marker. In this case, recombinant formation was found to be partially dependent upon ruvC function, especially in a recG mutant background. In a third type of experiment, the recombining partners were the host cell chromosome and a 4-kb linear DNA fragment containing the cat gene, with flanking lac sequences, released from the infecting phage chromosome by restriction enzyme cleavage in the cell; the formation of chloramphenicol-resistant bacterial progeny was measured. Dependence on RuvC varied considerably among the three types of cross. However, in all cases, the frequency of Red-mediated recombination was higher in recG than in recG+. These observations favor models in which RecG tends to push invading 3'-ended strands back out of recombination intermediates.

Kinetic characterization of the GTPase activity of phage lambda terminase: evidence for communication between the two "NTPase" catalytic sites of the enzyme.

Abstract: The terminase enzyme from bacteriophage λ is responsible for the insertion of viral DNA into the confined space within the capsid. The enzyme is composed of the virally encoded proteins gpA (73.3 k...

Two-hybrid assay: construction of an Escherichia coli system to quantify homodimerization ability in vivo

Abstract: A hybrid system which takes advantage of the properties of the lambda repressor allows detection of protein-protein interactions. Fusion of the cI N-terminal domain to a heterologous protein will result in a functional lambda repressor, able to strongly bind to its operator and conferring immunity to lambda infection only when the heterologous protein dimerizes efficiently. In this paper, construction of a recombinant plasmid which allows detection of the activity of the lambda chimeric repressor formed by the N-terminal part of cI fused with a heterologous protein is reported. This construct is interesting due to its potential to be integrated in any target gene of the bacterial host, thus permitting this hybrid assay to be performed, not only in Escherichia coli strains, but in every bacterial genus where the reporter gene can be expressed. In addition, because of its modular construction, this plasmid can be easily modified to be exploitable in many experimental situations, such as in the detection of promoter region activity.

Heat-inactivation of plasmid-encoded CI857 repressor induces gene expression from Ind- lambda prophage in recombinant Escherichia coli

Abstract: We have observed significant cell lysis upon temperature up-shift of recombinant Escherichia coli cultures harboring CI857-repressed lambda-based expression vectors. This event, that becomes evident about 30-40 min after the heat shock, takes place when using the lambda promoter system in Ind- lysogenic strains, but not in others commonly employed for recombinant gene expression. These results strongly suggest that the thermosensitive CI857 repressor, encoded by the expression vector, competes with CI Ind- molecules for binding to the prophage operator region, allowing for expression of lytic genes from the integrated Ind- viral genome upon temperature up-shift. Transcription of viral lytic genes does not include unspecific expression of a reporter sulA::lacZ gene fusion carried in the prophage genome. These results prompt, however, to carefully evaluate the limitations of expression systems based on pL/pR-CI857 in bacterial strains modified through lambda Ind- gene transfer vehicles.

Translational frameshift sites within bacteriophage lambda genes rexA and cI.

Abstract: Phage lambda's cI-rexA-rexB operon displays an intriguing example of regulation by an unexplained mechanism of polarity. We have identified three potential -1 translational frameshift sites and present a model for translational frameshift suppression by lambda's CI repressor as a mechanism of regulating operon polarity, implying an additional role for CI self-regulation.

Overexpressions of Lambda Phage Lysis Genes and Biosynthetic Genes of Poly-β-hydroxybutyrate in Recombinant E.coli

Abstract: ＩｎｔｒｏｄｕｃｔｉｏｎＰｏｌｙβｈｙｄｒｏｘｙｂｕｔｙｒａｔｅ（ＰＨＢ）ｉｓａｋｉｎｄｏｆｂｉｏｄｅｇｒａｄａｂｌｅｐｌａｓｔｉｃｓａｃｃｕｍｕｌａｔｅｄａｓｇｒａｎｕｌｅｓｉｎｃｅｌｓ．Ｔｈｅｆｉｒｓｔｓｔｅｐｔｏｓｅｐａｒａｔｅｉｔｉｓｃｅ...