Interactions between phage lambda replication proteins, lambda DNA and minicell membrane

Aberrant regulation of synthesis and degradation of viral proteins in coliphage lambda-infected UV-irradiated cells and in minicells

The patterns of bacteriophage lambda proteins synthesized in UV-irradiated Escherichia coli cells and in anucleate minicells are significantly different; both systems exhibit aberrations of regulation in lambda gene expression. In unirradiated cells or cells irradiated with low UV doses (less than 600 J/m2), regulation of lambda protein synthesis is controlled by the regulatory proteins CI, N, CII, CIII, Cro, and Q. As the UV dose increases, activation of transcription of the cI, rexA, and int genes by CII and CIII proteins fails to occur and early protein synthesis, normally inhibited by the action of Cro, continues. After high UV doses (greater than 2,000 J/m2), late lambda protein synthesis does not occur. Progression through the sequence of regulatory steps in lambda gene expression is slower in infected minicells. In minicells, there is no detectable cII- and cIII-dependent synthesis of CI, RexA, or Int proteins and inhibition of early protein synthesis by Cro activity is always incomplete. The synthesis of early b region proteins is not subject to control by CI, N, or Cro proteins, and evidence is presented suggesting that, in minicells, transcription of the early b region is initiated at a promoter(s) within the b region. Proteolytic cleavage of the regulatory proteins O and N and of the capsid proteins C, B, and Nu3 is much reduced in infected minicells. Exposure of minicells to very high UV doses before infection does not completely inhibit late lambda protein synthesis.

DNA-protein interactions during replication of genetic elements of bacteria

Specific interactions of DNA with proteins are required for both the replication of deoxyribonucleic acid proper and its regulation. Genetic elements of bacteria, their extrachromosomal elements in particular, represent a suitable model system for studies of these processes at the molecular level. In addition to replication enzymes (DNA polymerases), a series of other protein factors (e.g. topoisomerases, DNA unwinding enzymes, and DNA binding proteins) are involved in the replication of the chromosomal, phage and plasmid DNA. Specific interactions of proteins with DNA are particularly important in the regulation of initiation of DNA synthesis. Association of DNAs with the cell membrane also plays an important role in their replication in bacteria.

Bacteriophage lambda replication proteins: formation of a mixed oligomer and binding to the origin of lambda DNA

The purified bacteriophage lambda replication proteins O and P sediment separately in metrizamide gradients of low ionic strength as dimers. Together they interact with each other forming an oligomer, composed of two molecules of lambda O and one molecule of lambda P. The lambda O-P oligomer is active in the in vitro replication of ori lambda-containing DNA. Equilibrium sedimentation in preformed metrizamide density gradients under conditions that separate DNA-protein complexes from free proteins was employed in order to study possible interactions among the lambda replication proteins and ori lambda DNA. It was found that the lambda P protein binds specifically to ori lambda-containing plasmid DNA only in the presence of lambda O protein. About 100 molecules of lambda O and 10 molecules of lambda P form a complex with the ori lambda DNA. The lambda DNA-lambda O-lambda P complex was shown to be active in an in vitro replication system. Since the physical interactions between ori lambda and lambda O and between lambda P and the Escherichia coli dnaB replication protein are well documented, the evidence for a lambda O-P interaction presented in this paper provides the missing link in the molecular mechanism that enables lambda to direct the host replication machinery to the replication of its own DNA.

Escherichia coli dnaJ- and dnaK-gene products: synthesis in minicells and membrane-affinity

Escherichia coli dnaJ- and dnaK-gene products have been identified in a system of minicells infected with the appropriate transducing lambda phages. The molecular weights of these polypeptides in dodecyl sulphate/acrylamide electrophoresis amounted to 39,000 and 77,000, respectively. Equilibrium sedimentation of minicell lysates in metrizamide density gradients has revealed that both these host proteins, indispensable for lambda DNA replication, are membrane-bound.

Bacteriophage lambda initiators: preparation from a strain that overproduces the O and P proteins

A recombinant plasmid was constructed which carries bacteriophage lambda initiator genes O and P under control of tandemly arranged PL and PR promoters. These promoters were repressed by a thermosensitive repressor, cI857, at low temperature, but became active when the culture was incubated at 42 degrees C. Upon elevation of the temperature, the O and P proteins were overproduced to the extent that they constituted several per cent of the total E. coli cellular proteins. Both the O and P proteins have been purified to apparent homogeneity, and were shown to consist of 298 and 233 amino acid residues, respectively. The amino acid composition and the terminal partial amino acid sequence of each protein were determined. Through these analyses, the locations of the O and P genes in the known lambda DNA sequence were determined. The termination codon for the O gene overlaps with the initiation codon for the P gene. The purified O protein binds specifically to the replication origin of lambda (lambda ori) in accordance with our previous observations. The purified P protein inhibits an ATPase activity of dnaB protein.