Involvement of some host function of Escherichia coli in the turn off control of phages phi 80 and lambda

New preclinical models for angioimmunoblastic T-cell lymphoma: filling the GAP

Mouse models are essential to study and comprehend normal and malignant hematopoiesis. The ideal preclinical model should mimic closely the human malignancy. This means that these mice should recapitulate the clinical behavior of the human diseases such as cancer and therapeutic responses with high reproducibility. In addition, the genetic mutational status, the cell phenotype, the microenvironment of the tumor and the time until tumor development occurs, should be mimicked in a preclinical model. This has been particularly challenging for human angioimmunoblastic lymphoma (AITL), one of the most prominent forms of peripheral T-cell lymphomas. A complex network of interactions between AITL tumor cells and the various cells of the tumor microenvironment has impeded the study of AITL pathogenesis in vitro. Very recently, new mouse models that recapitulate faithfully the major features of human AITL disease have been developed. Here, we provide a summary of the pathology, the transcriptional profile and genetic and immune-phenotypic features of human AITL. In addition, we give an overview of preclinical models that recapitulate more or less faithfully human AITL characteristics and pathology. These recently engineered mouse models were essential in the evaluation of novel therapeutic agents for possible treatment of AITL, a malignancy in urgent need of new treatment options.

Construction and characterization of plasmid and lambda phage vector systems for study of transcriptional control in Escherichia coli

We constructed a family of lambda phage and plasmid vectors which facilitate cloning and quantitative analysis of transcriptional regulator in both single and multiple copies. Their expression system was modified from the ara-trp-lac fusion operon of plasmid pMC81 [Casadaban and Cohen, J. Mol. Biol. 138 (1980) 179-207], which is designed to assay both promoters and terminators with a single vehicle. To eliminate transcriptional and translational polar effects liable to occur in the original fusion operon upon insertion of a foreign nucleotide sequence, intracistronic Rho-dependent terminators, that are present within the trpB gene and distal to the cloning site were deleted, and DNA spacers containing stop codons were introduced immediately before and after the cloning site. In analysis of the cloned trp regulatory region, the lambda phage system faithfully reproduced the tight regulation by tryptophan characteristic to the natural trp operon on the E. coli chromosome, whereas the plasmid counterpart exhibited a substantially relaxed response. Comparative studies on the relative strengths of various promoters and terminators have further demonstrated that the lambda phage vector system permits accurate assays of exceptionally strong promoters like Ptrp and lambda pL without disturbing the bacterial growth, while being sensitive enough for detecting low-level transcription under the control of weak promoters or potent terminators. Cloning with the lambda phage vector can be greatly facilitated by transferring the target regulatory site precloned with the plasmid onto the phage genome through in vivo recombination.

Cloning of the exonuclease III gene of Escherichia coli

Overproducers of exonuclease III (exo III) were found within a colony bank containing ColE1-Escherichia coli hybrid plasmids. Through the enzymatic ligation of restriction enzyme fragments, the exo III gene, xth, was transferred to a thermoinducible, integration-proficient lambda phage and to a chimeric ColE1-lambda plasmid that was thermoinducible for lambda-directed DNA replication. Transfer of the xth gene was facilitated by a technique involving prior selection for Tn5 insertions into plasmid, thereby linking the gene to additional restriction sites and to a selectable (drug resistance) marker. After heat induction, cells bearing the thermoinducible ColE1-lambda-xth plasmid produced 120-fold more exo III than did plasmid-free cells. Enzyme production was not further enhanced by any of the following chromosomal mutations: dnaA, recBC, tob, or nusA snu. Several observations suggested that enzyme over-synthesis was the result primarily of lambda-detected replication rather than lambda-directed transcription.

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.

Isolation and genetic characterization of the nitA mutants of Escherichia coli affecting the termination factor rho

Taking advantage of the Spi (sensitivity to P2 interference) phenomenon, bacterial mutants seemingly resistant to phage lambdasusNnin5, but sensitive to phage lambdaspi, were isolated from a strain of E. coli K12 carrying no nonsense suppressor and lysogenic for P2. A class of these mutants, designated nitA (N-independent transcription), is described here. Upon infection of the nitA mutants with a trp transducing phage lambdasusN7N53ptrp46 which carries the E. coli trpE and D genes in the CIII-att region of the lambda genome, formation of anthranilate synthetase (ASase, a complex protein of trp E and D gene products) was clearly demonstrated. In contrast, no ASase formation was observed in the parent nitA+ strain under the same conditions. The synthesis is subject to "turn off" control, and is completely repressed by the CI repressor of phage lambda. The nitA cells lysogenic for lambdaCI857susN7N53 are killed by thermal induction much more efficiently than the parent cells lysogenic for the same phage. The nitA mutants support the growth of lambdasusN7N53byp much better than the parent. These results suggest that the nitA mutation permits the early leftward and rightward transcription of the lambda genome in the absence of the N gene product. On the E. coli genetic map, nitA is located between ilv and metE, nearer to ilv. The mutant allele is recessive to the wild-type allele. The present evidence, together with results of biochemical investigations to be reported, suggests that nitA is a gene specifying the transcription termination factor rho.