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Biomedical subjects

I Hertman

Publications and source records attributed to I Hertman.

At least 19 recordsLinked to original sources
PubMed1987

Identification and characterization of the functional alpha origin of DNA replication of the R6K plasmid and its relatedness to the R6K beta and gamma origins.

The functional R6K alpha origin is composed of two DNA elements, one of 580 bp carrying the alpha origin sequences and the other of 277 bp containing the seven 22 bp direct repeats previously identified as also required for gamma and beta origin activity. These two genetic elements are separated by approximately 3,000 bp of R6K sequences which are dispensable for alpha origin activity. The function of the alpha origin depends on the presence in cis of the 580 bp and the 277 bp fragments and requires that they be oriented as in the intact R6K. Activation of the alpha origin depends on the R6K replication initiation protein pi. Within the 580 bp of the alpha origin, there is a sequence of 98 bp which appears as an inverted repeat of 96 bp in the beta replicon. Deletion of the 96 bp or 98 bp results in inactivation of the alpha and the beta origins respectively. These long repeats are palindromic and it is suggested that these may serve as the recognition signals for initiation of DNA replication in the alpha and the beta origins of R6K. DNA homology analysis performed on alpha, beta and gamma origin sequences, also reveals 10-23 bp sequences in the alpha and the beta origins that are related to the family of 22 bp direct repeats in the gamma origin which were shown previously to be binding sites for the pi protein.

Base Sequence↗
PubMed1987

Molecular aspects of genetic instability of an artificial 68 bp perfect palindrome in Escherichia coli.

An artificial 68 bp perfect palindrome carried on a plasmid (pAS807) is genetically unstable. An increase in the population of cells harbouring palindrome-deleted pAS807 derivatives (pAS807-V) is observed as the number of cell generations increases. The calculated frequency of palindrome excision events per cell generation and per plasmid replication round in Escherichia coli is 0.95 X 10(-4). Sequence analysis of eight independent isolates of palindrome-deleted molecules, reveals two symmetrical deletion types (three of type I and five of type II). The two types of pAS807-v molecules retain 19 bp of the original sequence of the 68 bp palindrome but differ in the content of the central 3 bp. The generation of the two deletion types is best explained by formation of intermediate cruciform structures. Following the fate of the palindrome in various bacterial mutants, we find that the excision events depend on functional polA1, polA(ex1), lig, texA343(recC343) and texA344(recB344) gene products. However, recB21 recC22 mutations do not affect palindrome excision.

Base Sequence↗
PubMed1985

Penicillinase plasmid-linked genetic determinants for enterotoxins B and C1 production in Staphylococcus aureus.

The genes encoding for beta-lactamase (bla+) and resistance to metallic ions (cadmium, mercury, lead, arsenate, and arsenite) were located in a 56.2-kilobase plasmid, pZA10, isolated from a clinical strain, Staphylococcus aureus 6344. This strain produced enterotoxin B and enterotoxin C1. Elimination of pZA10 by either sodium dodecyl sulfate or heat treatment (43 degrees C) resulted in the loss of the capability of the bacteria to produce both enterotoxin B and enterotoxin C1. A physical map of pZA10 was constructed with BamHI, SalI and BglII restriction endonucleases. Penicillin-resistant, enterotoxin B- and C1-producing cotransformants were isolated by transformation with pZA10 DNA with either S. aureus RN450 or cured S. aureus 6344 as recipients. The transferred plasmids exhibited genetic instability shown by changes in restriction pattern and molecular size, loss of plasmid DNA, and addition of chromosomal DNA. Enterotoxin B production was related to a 18.1-kilobase pZA10 fragment carried by such a rearranged plasmid. Chromosomal cointegration of bla+ with genetic determinants for metallic ion resistance and enterotoxin B and C1 production were detected in heat-treated S. aureus 6344. Transformation employing chromosomal DNA containing the integrated plasmid resulted in excision and reestablishment of pZA10-related plasmids in the transformants. pZA10-linked resistance to cadmium, which was lost upon the integration of pZA10 into the host chromosome, reappeared in transformants carrying the excised plasmid.

Bacterial Proteins↗
PubMed1983

Genetic instability of an artificial palindrom DNA sequence.

A short DNA palindrom, produced by head to head ligation of a 29 bp DNA fragment, was inserted into a 27,000 bp plasmid DNA element composed of two functional replicons (R6K, ColE1). Several plasmid types containing a single copy of this palindrom in different locations of insertion on the R6K sequence were obtained. The palindrom was engineered to possess a unique EcoRI recognition sequence at its axis of symmetry. The presence of this restriction site allowed to monitor the genetic stability of the artificial palindrom at their different insertion loci. Out of 5 different insertion locations, one (in pAS807) was found to lead to a significant destabilization of the palindrom. This insertion site lies within the replication control region of R6K. We have shown that the inserted palindrom in pAS8O7 does not affect the functionality of the R6K replication origins. Excission of the palindrom sequences from pAS8O7 was not accompanied by loss of the adjacent R6K DNA sequences. Different deletion derivatives of pAS807 were generated in-vitro in order to determine the driving unit of DNA sequences around the palindrom that are involved in its excision. The results imply that large DNA structure(s) around the palindrom are involved in its excission. Complete deletion of R6K sequences from either the left or the right side of the palindrom resulted in new configurations which stabilized the palindrom. A configuration of R6K DNA sequences exceeding 270 bp long sequence from both sides of the palindrom are necessary for the transition from a palindrom stable to palindrom unstable state. In addition evidence is presented to show that the excision process of palindrom sequences requires a functional polymerase I but not the gene product of recA.

Base Sequence↗
PubMed1983

Postincision steps of photoproduct removal in a mutant of Bacillus cereus 569 that produces UV-sensitive spores.

An excision-defective mutant of Bacillus cereus 569 is normal in incision and repair synthesis, but rejoining of incision breaks is defective, resulting in accumulation of low-molecular-weight DNA after UV irradiation. The defect in removal of photoproducts by exonuclease after incision renders both vegetative cells and dormant spores of the mutant sensitive to UV. A similarity is indicated to the uvrD mutation described recently in Escherichia coli.

Bacillus cereus↗
PubMed1980

A vaccine strain of Pasteurella multocida obtained by mutagenesis.

A virulent avian septicemia strain of Pasteurella multocida (P. multocida) serotype 1 was mutagenized with N-methyl-N'-nitro-N-nitroso guanidine. A selection procedure was devised to isolate mutants with changed growth properties. Mutants were isolated that had either prolonged doubling time or temperature sensitivity for growth at 41 degrees C. A correlation was observed between growth properties in vitro and multiplication in vivo. Mutants defective in growth were avirulent. A positive correlation was observed between the rates of multiplication of mutant strains in vitro and their ability to protect against heterologous challenge.

Animals↗
PubMed1978

Cleavage maps of a tetracycline plasmid from Staphylococcus aureus.

The cleavage maps of a Staphylococcus aureus plasmid, pSN1 (2.75 megadaltons), conferring tetracycline resistance, were determined. Cleavage maps are given for HpaI and HindIII restriction endonucleases by using the single HpaII site as a reference point. Nucleases EcoRI, BamHI, SalI, and HaeIII have no sites on this plasmid.

DNA Restriction Enzymes↗
PubMed1977

Isolation and characterization of a plasmid involved with enterotoxin B production in Staphylococcus aureus.

Genetic analysis and molecular characterization of plasmid deoxyribonucleic acid (DNA) was performed in a toxigenic isolate of Staphylococcus aureus strain DU4916. Elimination, transduction, and transformation experiments provided us with a series of derivatives similar except for the presence or absence of genes mediating resistance to penicillin (penr), methicillin (mecr), and tetracycline (tetr) and enterotoxin type B (SEB) production (entB+). The derivatives were examined for the presence of a plasmid species which encodes for SEB production. Two distinct species of covalently closed circular DNA of about 2.8 X 10(6) and 0.75 X 10(6) daltons were identified in an ethidium bromide-cured, penicillinase-negative (pens) isolate, SN109 (mecr tetr emtB+). Further segregation of either methicillin resistance or tetracycline resistance or of both together resulted in the loss of SEB production and the disappearance of both plasmids. Transduction from strain SN109 showed that determinants for tetracycline resistance are carried by the 2.8 X 10(6) dalton plasmid. Transformation with covalently closed circular DNA from strain SN109 yielded mecs tetr entB- transformants harboring the tetracycline resistance plasmid alone and mecr tetr entB+ transformants harboring both the tetracycline resistance and the 0.75 X 10(6)-dalton plasmid. Further segregation of methicillin resistance in transformants was not associated with any change in plasmid DNA. The results indicate that a genetic determinant for SEB production is carried by the 0.75 X 10(6)-dalton plasmid. It is possible, however, that this plasmid cannot be maintained in the host independently from the tetracycline resistance plasmid. Methicillin resistance in the strains examined could not be ascribed to any of the covalently closed circular DNA components resolved in strain DU4916.

Anti-Bacterial Agents↗
PubMedDate not supplied

Attenuated live fowl cholera vaccine. I. Development of vaccine strain M3G of Pasteurella multocida.

A live cholera vaccine was developed from a virulent avian septicemia strain of Pasteurella multocida serotype 1. The virulent parental strain was mutagenized with N-methyl-N'-nitro-N-nitroso guanidine. Mutants were selected that had either smaller colonies at 37 C or temperature sensitivity for growth at 41 C. Four small-colony mutants and 2 temperature-sensitive mutants were studied. All the mutants were avirulent for turkeys. Sixteen days after turkeys were vaccinated with each mutant, both the vaccinates and unvaccinated controls were challenge-exposed to virulent P. multocida of the homologous serotype and the heterologous serotype 3. Two of the small-colony mutant strains protected against both homologous and heterologous challenge. Suggested for a live cholera vaccine is P. multocida M3G, a small-colony-forming mutant, innocuous for both mice and turkeys and stable against reversion.

Animals↗