Repression by the cI protein of phage lambda: interaction with RNA polymerase

Identification of operator sites of the CI repressor of phage TP901-1: evolutionary link to other phages

The repressor encoded by the cI gene of the temperate Lactococcus lactis subsp. cremoris bacteriophage TP901-1 has been purified. Gel-retardation and footprinting analyses identified three palindromic operator sites (O(R), O(L), and O(D)). The operator site O(R) is located between the two divergent early promoters P(R) and P(L), O(L) overlaps the transcriptional start of the lytic P(L) promoter, and O(D) is located downstream of the mor gene, the first gene in the lytic gene cluster. The function of O(L) was verified by mutational analysis. Binding was found to be specific and cooperative. Multimeric forms of the repressor were observed, thus indicating that the repressor may bind simultaneously to all three operator sites. Inverted repeats with homology to the operator sites of TP901-1 were identified in phage genomes encoding repressors homologous to CI of TP901-1. Interestingly, the locations of these repeats on the phage genomes correspond to those found in TP901-1, indicating that the same system of cooperative repression of early phage promoters has been inherited by modular evolution.

Purification and some properties of presumptive tof gene product of Coli phage 434

The presumptive tof gene product of Coli phage 434 has been purified from cells carrying lambdaimm434cIdv plasmid known to contain only some of the "early" genes of phage 434 and lambda. It was detected and tentatively identified as tof protein primarily by its ability to specifically bind to phage 434 DNA. The protein has a molecular weight of about 11,000 and requires Mg2+ for specific DNA binding, unlike 434 cI-repressor.

Heat-sensitive DNA-binding activity of the cI product of bacteriophage lambda

The binding of lambda gene cI product to lambda DNA was studied at temperatures from 0 degrees C to 46 degrees C. Binding activity of the products of cIts mutants was higher at 22 degrees C than at 0 degrees C, 26 degrees C or 30 degrees C. Both cI+ and cIts products lost DNA-binding activity at 46 degrees C, but after subsequent cooling to 22 degrees C, they regained 50-100% of their activity.

Multiple repressor binding at the operators in bacteriophage lambda

Short DNA duplexes are protected when lambda DNA is digested with nuclease in the presence of lambda repressor. As the ratio of repressor to operator is increased, six successively larger fragments are recovered, ranging in size from 35 to 100 base pairs, each of which binds repressor. Study of these fragments indicates that, at each of the two lambda operators (o(L) and o(R)), repressor first binds to a unique site (not necessarily terminal), and that five additional sites are then filled in linear right-ward or left-ward order. The nucleotide sequences and affinities for repressor of o(L) and o(R) are not identical, although six fragments of similar size are protected at each operator. Evidence is presented arguing against the existence of hairpin-like structures in the operator fragments, and, moreover, it is shown that the operator duplex does not unwind when repressor binds to it.

Purification and properties of D protein: a transcription factor of Escherichia coli

D factor is protein that stimulates DNA transcription in vitro by RNA polymerase. For DNA from bacteriophage lambda, we present evidence that D protein interacts with DNA to increase the frequency and improve the specificity of initiation by RNA polymerase.