Interaction of the operator of the tryptophan operon with repressor

Transcription studies in vitro on repression of the tryptophan operon of Escherichia coli show that partially purified trp repressor binds specifically to DNA containing the trp operator with a repressor-operator dissociation constant of about 0.2 nM in 0.12 M salt at 37 degrees , a value consistent with the extent of trp operon regulation in vivo. The half-life of the trp repressor-trp operator complex is less than 2 min in vitro in 0.12 M salt.

Escherichia coli RNA-polymerase binding sites on DNA are only 14 base pairs long and are located between sequences that are very rich in AplusT

E. coli DNA-dependent RNA-polymerase binding sites on DNAs of T5, T7, and lambda coliphages have been isolated according to three different methods in order to analyze the binding sites themselves as well as the nearest neighboring regions. It is shown that the binding sites are regions that are rather rich in G+C, are about 14 base pairs long and are located between DNA sequences highly enriched in A+T. The biological implications of this result are discussed.

Synergistic interactions of T4 early proteins concerned with their binding to DNA

Under appropriate conditions, 19 distinct early proteins produced by bacteriophage T4 bind DNA with various affinities. They include products of genes that have been implicated in T4 DNA metabolism, such as DNA negative, DNA arrest, and DNA delay genes, and others whose roles have not yet been defined. The identifiable DNA-binding proteins are the products of genes 43, rIIA, 46, 30, 39, 52, betagt, 32, and internal protein III. In some cases, protein-protein interactions are involved in the formation of the DNA-protein complexes.

Activity of empty, headlike particles for packaging of DNA of bacteriophage lambda in vitro

A precursor head of phage lambda is synthesized after induction of cells lysogenic for lambdaD(-)F(-) and lambdaA(-) (head-defective) mutants. This precursor head can be assayed by complementation in vitro and can be purified by CsCl gradient centrifugation and sucrose gradient sedimentation. The precursor head contains no DNA and has the same dimensions as the petit lambda particle. It can be packed with lambda DNA in an extract from induced Escherichia coli lysogenic for a lambdaE(-) mutant.

In vitro repair of apurinic sites in DNA

Apurinic sites disappear from DNA during an incubation of the DNA with the Escherichia coli endonuclease specific for apurinic sites, DNA polymerase I (EC 2.7.7.7.), and T4 ligase (EC 6.5.1.1). Omission of any one of these three enzymes and, in particular, omission of the endonuclease specific for apurinic sites prevents this in vitro repair.

In vitro genetic recombination of bacteriophage lambda

DNA of bacteriophage lambda recombines in a cell-free extract prepared from an induced Escherichia coli lysogen of bacteriophage lambda. The assay for recombination in vitro takes advantage of the ability of such an extract to package lambda DNA and to assemble complete phage particles. For example, when lambda DNA that has been extracted from phage with the immunity of 434 is added to an extract, infectious lambda imm 434 particles are produced. The precursor DNA molecule in this packaging reaction is a multichromosomal polymer; circular monomers, for example, are not packaged.Nevertheless, when 434 circular DNA monomers are added to an extract, some phage that contain the imm 434 marker are produced. In this case, the circular DNA had recombined with lambda DNA in the extract and thereby had become part of a polymeric structure, which by the normal packaging process could give rise to infectious particles with the imm 434 marker. Genetic recombination is demonstrated when imm 434 circular monomer DNA carries amber mutations in genes A and B; then most of the 434 plaque formers produced in vitro are A(+)B(+), the genotype of the endogenous lambda DNA. Genetic crossing-over occurs through a region that contains the prophage attachment site, suggesting that recombination is carried out by the lambda Int functions. The 434 recombinant plaque formers are particles physically identical to wild-type 434 particles, as judged by their buoyant density in a CsCl equilibrium gradient.

Release of polarity in Escherichia coli by gene N of phage lambda: termination and antitermination of transcription

The induction of lambda prophage provokes the constitutive expression of the adjacent gal operon in E. coli. This "escape synthesis" can result from transcription that initiates at a phage promoter and extends into the gal operon. The effect requires the product of the lambda gene N. N-mediated transcription not only fails to terminate at the prophage-bacterial junction and at the ends of bacterial operons, but ignores termination signals caused by polar insertions or ochre mutations within gal. Suppression of polarity by N-function is a cis-effect; only transcription initiated at the phage promoter is influenced. We propose that the transcription complex is influenced by N-product to become termination-resistant at a site in the phage genome (juggernaut model). This site appears to be at or near the phage promoter.

Protein fusion: a novel reaction in bacteriophage lambda head assembly

Parts of two phage-coded head proteins, pE and pC, become fused during bacteriophage lambda head assembly. pE is the main structural component of lambda heads and pC is a minor head protein that is not found as such in mature heads. The bond joining the two proteins appears to be covalent and is not a disulfide bond. Only a specific subset of the sequences of each protein is found in the fusion products, and these sequences are found in the products in equimolar amounts. Two nearly identical fusion products; X1 and X2, are detected; X2 is slightly smaller than X1 and appears to be a proteolytic cleavage product of X1. The fusion reaction probably takes place on a nascent head structure.

The roles of the lambda c3 gene and the Escherichia coli catabolite gene activation system in the establishment of lysogeny by bacteriophage lambda

Maximum lysogenization of E. coli by bacteriophage lambda requires both the lambdacIII gene function and the host catabolite gene activation system mediated by adenosine 3':5'-cyclic monophosphate. Whereas considerable lysogenization occurs in the presence of either system alone, lysogenization is absolutely prevented in the absence of both systems. Neither system is, however, required for efficient lysogenization when the host bears an hfl(-) mutation. It is argued that the normal function of these two systems is to negate the antagonistic effect of the Hfl(+) protein upon lysogenization. It is further argued that both the lambdacIII gene function and the Hfl(+) protein do not directly affect the host catabolite gene activation system.

A preliminary map of the major transcription units read by T7 RNA polymerase on the T7 and T3 bacteriophage chromosomes

Transcription of T7 DNA by T7 RNA polymerase in vitro gives rise to six major size classes of RNAs comprising seven major T7 RNA species. These RNAs are all read from the r-strand of T7 DNA and are not derived from the early (leftmost on the conventional genetic map) region of the molecule. When artifically shortened T7 DNA templates are transcribed, four (I, II, IIIb, and VI) of the seven species are found to be truncated or deleted. This indicates that all are terminated near the right end of the T7 DNA molecule, probably at a common termination site near 98.5%. (Map positions are all given in terms of percentage of total length measured from the left end of the molecule.) Since the approximate lengths of the transcripts are known, the promotor sites for T7 RNA species I, II, IIIb, and VI are tentatively mapped at 56, 64, 83, and 97% on the T7 chromosome. Only a single major T3 RNA is transcribed by T7 RNA polymerase; analysis of transcripts directed by shortened T3 DNA templates indicates it is analogous to T7 RNA species IIIb. Hence the promotor and terminator sites for T3 species IIIb are tentatively mapped at 83 and 98.5%, respectively, on the T3 chromosome. The major transcripts read by T7 RNA polymerase from T3-T7 hybrid phage DNAs vary, depending on which regions of the T7 chromosome are present. This provides an alternative method of mapping the strong T7 promotor sites on the T7 chromosome.

In vivo repair of the single-strand interruptions contained in bacteriophage T5 DNA

Bacteriophage T5 is known to contain several unique single-strand interruptions in only one strand of the duplex DNA. Analysis of labeled parental phage DNA from infected Escherichia coli shows that these nicks are repaired in vivo to yield intact double-stranded molecules. Sealing begins at about 6 min after infection and is independent of DNA replication. Repair may be an ordered process that starts at a unique end of the molecule.