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At least 109 records · Page 6Linked to original sources
PubMed1976

Control of cI gene expression in bacteriophage lambda imm434, studied in an immunity/trp fusion made in vitro.

The trp genes of a lambda imm434 trp-transducing phage have been fused to the immunity region by deletion, in vitro, of the DNA between two targets for the restriction enzyme R.EcoRI. The resulting phage has been used to study the control of expression of the cI gene in vivo. The constitutive rate of expression of the cI gene is between 2 and 5% of the maximally stimulated rate. The products of the cII and cIII genes enhance expression of cI on infection of a sensitive host. The requirement for the cII product is more stringent than that for the cIII protein. The phage 434 repressor present in a 434-immune cell stimulates the rate of cI expression from a superinfecting homoimmune phage about fifteen-fold. This result strongly suggests that repressor stimulates its own synthesis by a direct effect on transcription of the cI gene.

Chromosome Mapping↗
PubMed1979

The isolation and characterisation of a plaque-forming derivative of bacteriophage Mu carrying a fragment of Tn3 conferring ampicillin resistance.

We have isolated a plaque-forming derivative of phage Mu which carries a determinant for ApR. The biological properties of this MuAp phage are similar to those of normal Mu. Its genome contains a 1.1 kb substitution where Mu DNA from the right end of the G region has been replaced by a similar length of DNA from the transposon Tn3. This fragment of Tn3 DNA carries the ApR gene, but is no longer capable of independent transposition.

Ampicillin↗
PubMed1976

Isolation and characterization of phi80dgal transducing phages that carry gal operator-promoter insertion mutations.

phi80dgal transducing bacteriophages have been isolated by the F-fusion technique of Press et al. (1971) and gal-operator-promoter insertion mutations have been introduced by homogenate formation. Five different phi80dgal isolates have been studied in more detail. One of the phi80 phages transduces the gal operon and gene aroG as well as at least part of the trp-operon; the gal operon of another phi80dgal transducing phage is inverted with respect to the phi80dgal sequences. Heteroduplex DNA mapping indicates that one of the phi80dgal isolates in addition to the gal operon and a portion of the adjacent chromosomal region carries an IS2-element which is derived from the F'gal episome. The isolated phi80dgal phages may be utilized for preparing pure gal mRNA and insertion-RNA as well as pure gal operon DNA.

Coliphages↗
PubMed1977

Overproducing araC protein with lambda-arabinose transducing phage.

Escherichia coli infected with bacteriophage lambda-arabinose transducing phage were tested as sources of araC protein. Infection of cells with such phage produces an intracellular concentration of araC protein up to 100 times that present in wild-type E. coli, apparently resulting from fusion of the araC gene to bacteriophage lambda promoters. Lysates from these phage-infected cells may be fractionated to yield another 100-fold enrichment in araC activity so that the total enrichment is 10,000-fold. A nonsense mutation in araC provided proof of the identification on gel electrophoresis of a band in the purified material. Biologically active araC protein is a dimer with 28,000 M.W. subunits. The araC gene in these phage replaces the int-xis genes but is oriented in the opposite direction. Nonetheless, it appears to be transcribed in this position by the phage promoter pr via transcription the long way around. Furthermore, because araC gene is in this position, we were able to isolate phage on which the araC gene was under phage late gene control by deletion of the late gene transcription stop signals in the b2 region.

Arabinose↗
PubMed1975

Escherichia coli mutants uvr D and uvr E deficient in gene conversion of lambda-heteroduplexes.

Calcium-treated cells of E. coli K-12 C600 were transfected with lambda-heteroduplex DNA carrying the marker cIts857 in one strand and wildtype in the other. In single burst analyses of the phage progeny, 72-79% of the bursts were "pure" bursts containing either exclusively wildtype phage or exclusively mutant phage, indicating that conversion of the cIts857/+ mismatch to a homoduplex structure prior to replication occurred with this frequency. The r-strand1 appears to be "preferred", since pure bursts of progeny with the r-strand genotype were almost twice as frequent as those with the l-strand genotype. Examination of the conversion frequency of a number of rec and uvr E. coli mutants showed that the mutants uvr D and UVR E are deficient in mismatch repair. Conversion is reduced in the former by a factor of 2 and in the latter by a factor of 3.

Calcium↗
PubMed1975

Parameters of gene expression in the bipolar argECBH operon of E. coli K12. The question of translational control.

The pattern of divergent transcription of the argEC BH cluster of genes previously demonstrated by the hybridization of RNA to the separated strand of a phi 80 darg transducing phage, is confirmed with the DNA of a set of different lambdadarg phages. The accurate determination of argE and argCBH m-RNA levels in different steady states of expression of the arg regulon supports the following conclusions: 1. The ratio between maximal (derepressed) and minimal (repressed) rates of expression is lower when it is expressed in terms of % hybridizable RNA than in terms of expression is lower when it is expressed in terms of % hybridizable RNA than in terms of enzyme specific activities. The discrepancy is about 3 fold. Thus in conditions of repression, the cell produces relatively more unused m-RNA than in derepression. Different interpretations of this phenomenon appear possible: a) the messenger RNA molecules synthesized in repressed cells could be degraded more rapidly or translated less efficiently than in derepressed cells. b) an untranslated segment of the RNA could account for a larger part of the RNA detected in repression than in derepression. These interpretations are not mutually exclusive. 2. The discrepancy observed between the amplitudes of variation of argE and argC BH expression, expressed in terms of enzyme specific activities, is, in fact, determined at the level of DNA transcription. This provides direct evidence for the occurrence of differential transcription effectiveness in a regulon exhibiting a correlative but not strictly coordinated pattern of enzyme synthesis. This also supports our earlier suggestion regarding the possible complexity of the internal operator region situated between argE and C.

Arginine↗
PubMed1975

A mutant of Escherichia coli auxotrophic for organic phosphates: evidence for two defects in inorganic phosphate transport.

An inorganic phosphate transport mutant has been isolated as a sn-glycerol-3-phosphate auxotroph and characterized genetically. Two lesions are responsible for the transport defect. One lesion, pst, is located at minute 74 of the E. coli genetic map while the other lesion, pit, is located at minute 68. All "K10" strains that were examined carry the pit lesion. Evidence is presented that the glycerol phosphate and hexose phosphate transport systems are not important inorganic phophate transport systems. The mapping data indicate that the genetic distance between malA and xyl is greater than that now allowed.

Bacterial Proteins↗