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At least 757 records · Page 42Linked to original sources
PubMed1984

Structure and function of the repressor of bacteriophage lambda. II. Isolation and characterization of a lambda mutant which produces repressor having higher affinity for operators.

By mutagenizing a lambda cIts (lambda cI857) lysogen, a lambda mutant has been isolated with a wild-type phenotype. This mutant phage lysogenizes with low efficiency and produces a low burst. Though the initial rates of repressor synthesis in Escherichia coli after infection with wild-type and mutant lambda are the same, the maximum level of repressor that is synthesized in the latter case is only about 30% of that synthesized in the former. Virulent lambda plates on the lysogen of mutant lambda with slightly less efficiency producing very tiny plaques. Operator-binding studies made in vitro with purified mutant and wild-type repressors show that the binding curve of the former repressor is a rectangular hyperbola while that of the latter is sigmoid. The half-lives of the complexes of mutant and wild-type repressors with right operator are 133 and 27 min, respectively. All these results suggest that the mutant repressor possibly has a higher affinity for the operators. This mutant has been named lambda cIha (ha = high affinity).

Bacteriophage lambda↗
PubMed1996

Cleavage by RNase P of gene N mRNA reduces bacteriophage lambda burst size.

RNase P, an enzyme essential for tRNA biosynthesis, can be directed to cleave any RNA when the target RNA is in a complex with a short, complementary oligonucleotide called an external guide sequence (EGS). RNase P from Escherichia coli can cleave phage lambda N mRNA in vitro or in vivo when the mRNA is in a complex with an EGS. The EGS can either be separate from or covalently linked to M1 RNA, the catalytic RNA subunit of RNase P. The requirement for Mg2+ in the reaction in vitro is lower when the EGS is covalently linked to M1 RNA. Substrates made of DNA can also be cleaved by RNase P in vitro in complexes with RNA EGSs. When either kind of EGS construct is used in vivo, burst size of phage lambda is reduced by > or = 40%. Reduction in burst size depends on efficient expression of the EGS constructs. The product of phage lambda gene N appears to function in a stoichiometric fashion.

Bacteriophage lambda↗
PubMed1981

Arrangement of bacteriophage lambda receptor protein (LamB) in the cell surface of Escherichia coli: a reconstitution study.

The LamB protein purified in a solution of sodium dodecyl sulfate was assembled into an ordered hexagonal lattice structure with a lattice constant of about 7.8 nm in the presence of lipopolysaccharide. The LamB alone formed aggregates with some lattice structure. However, the regularity of the lattice was only maintained within a very small area. An ordered hexagonal lattice was also formed when the wild-type lipopolysaccharide was replaced by heptoseless lipopolysaccharide, lipid A, and even fatty acid. However, the lattice constants were appreciably smaller than that with the wild-type lipopolysaccharide. The results suggest that the heptose-containing polysaccharide region, as well as the fatty acid region, are involved in the interaction with the LamB protein. The LamB-lipopolysaccharide lattice was preferably formed on the peptidoglycan layer when the lipoprotein was covalently bound to this layer. These results indicate that the molecular arrangement of the LamB protein in the outer membrane is similar to that of matrix proteins, OmpC and OmpF, which exist as trimers. The ordered hexagonal lattice was active in the receptor function for lambda, resulting in phage adsorption and deoxyribonucleic acid ejection. Thus, this reconstitution system should provide a useful means of studying the mechanism of lambda infection.

Bacterial Outer Membrane Proteins↗
PubMed1979

[Hybrid plasmid pSD1 containing the immunity region of bacteriophage lambda].

Hybrid plasmid pSD1 carrying the immunity region of the coliphage lambda and bio operon have been obtained by means of studying the efficiency of transcription DNA fragments in the plasmid RSF2124. The molecular weight of this plasmid is 17.2 Md. The growth inhibition of phage lambdavir has been observed in cells carrying the new hybrid plasma. The properties of the plasmid pSD1 and probable reasons of the growth inhibition of phage lambdavir are discussed. The hybrid plasmid pSD2 carrying genes R, A and J of phage lambda has been constructed on the basis of the plasmid RSF2124. There are cohesive ends in this plasmid which make possible its packing in the phage lambda head. Hybrid plasmid pSD3 carrying genes P and Q of phage lambda has also been constructed.

Bacteriophage lambda↗
PubMed1997

Mutations affecting lysine-35 of gpNu1, the small subunit of bacteriophage lambda terminase, alter the strength and specificity of holoterminase interactions with DNA.

The small subunit of lambda terminase, gpNu1, contains a low-affinity ATPase activity that is stimulated by nonspecific dsDNA. The location of the gpNu1 ATPase center is suggested by a sequence match between gpNu1 (29-VLRGGGKG-36) and the phosphate-binding loop, or P-loop (GXXXXGKT/S), of known ATPase. The proposed P-loop of gpNu1 is just downstream of a putative helix-turn-helix DNA-binding motif, located between residues 5 and 24. Published work has shown that changing lysine-35 of the proposed P-loop of gpNu1 alters the response of the ATPase activity to DNA, as follows. The changes gpNu1 k35A and gpNu1 K35D increase the level of DNA required for maximal stimulation of the gpNu1 ATPase by factors of 2- and 10-fold, respectively. The maximally stimulated ATPase activities of the mutant enzymes are indistinguishable from that of the wild-type enzyme. In the present work, the effects of changing lysine-35 on the cos-cleavage and DNA-packaging activities of terminase were examined. In vitro, the gpNu1 K35A enzyme cleaved cos as efficiently as the wild-type enzyme, but required a 2-fold increased level of substrate DNA for saturation, suggesting a slight reduction in DNA affinity. In a crude DNA-packaging system using cleaved lambda DNA as substrate, the gpNu1 K35A enzyme had a 10-fold defect. In vivo, lambda Nu1 K35A showed a 2-fold reduction in cos cleavage, but no packaged DNA was detected. The primary defect of the gpNu1 K35A enzyme was concluded to be in a post-cos-cleavage step of DNA packaging. In in vitro cos-cleavage experiments, the gpNu1 K35D enzyme had a 10-fold increased requirement for saturation by substrate DNA. Furthermore, the cos-cleavage activity of gpNu1 K35D enzyme was strongly inhibited by the presence of nonspecific DNA, indicating that the gpNu1 K35D enzyme is unable to discriminate effectively between cos and nonspecific DNA. No cos cleavage was observed in vivo for lambda Nu1 K35D, a result consistent with the discrimination defect found in vitro for the gpNu1 K35D enzyme. In a crude packaging system the gpNu1 K35D enzyme had a 200-fold defect; in a purified packaging system, the gpNu1 K35D enzyme was found to be unable to discriminate between lambda DNA and nonspecific phage T7 DNA, a result indicating that the gpNu1 K35D enzyme is also defective in discriminating between lambda DNA and nonspecific DNA during DNA packaging.

Amino Acid Sequence↗
PubMed1987

[cAMP acceptor protein of Escherichia coli K-12 may be the repressor of the late promoter of bacteriophage lambda].

By computer analysis of the lambda phage DNA putative cAMP-CAP binding site has been found. This site (44506-AcgTGTGAccgcatTCAAAaT-44486) is located 40 bp upstream to the late PR' promoter. The sequence denoted is located on the coding DNA strand, similar to the cAMP-CAP binding sites in all four genes known to be subject to cAMP-CAP repression. It is suggested that cAMP-CAP can serve as a repressor of the phage lambda late promoter PR'. Such repression can arrest the expression of late lambda genes and in this way increase the frequency of lysogenization.

Bacteriophage lambda↗