Relationships among the streptothricin resistance transposons Tn1825 and Tn1826 and the trimethoprim resistance transposon Tn7

The streptothricin resistance transposons Tn1825 and Tn1826 are closely related, based on physical and genetic characteristics, to the trimethoprim resistance transposon Tn7. These transposons may be considered to be members of a transposon family sharing in common the transposition functions and a basic streptomycin/spectinomycin resistance determinant but differing from one another with respect to particular additional resistance genes inserted to the left of the aadA gene.     

Restriction map of Tn7

Tn7, a transposon of 14 kb, encodes resistance to trimethoprim (Tp) and streptomycin (Sm). A cleavage site map of this transposon for twenty-two different restriction enzymes as determined by comparison of restriction enzyme cleavage patterns of the plasmids ColE1 and ColE1::Tn7 is presented. The precise localization of these sites was facilitated by the use of two deletion derivatives of ColE1::Tn7: pGB2 and ColE1::Tn7Δ6, and by the use of pOB14 and pOB15 which contain a part of Tn7 cloned into the plasmid pBR322. This map should aid in the study of the structural and genetic organization of this transposon.     

Isolation and Characterization of Rifampin-Resistant and Streptolydigin-Resistant Mutants of Bacillus subtilis with Altered Sporulation Properties

Mutants of Bacillus subtilis with altered deoxyribonucleic-dependent ribonucleic acid polymerase activity have been isolated and characterized. These mutants, selected as strains resistant to rifampin or streptolydigin, demonstrate drug-resistant in vitro ribonucleic acid synthesis. Sporeforming ability and support of phage infection are altered in many of the mutants. Mutations to rifampin and streptolydigin resistance have been located on the B. subtilis chromosome and ordered relative to the markers cysA14 and str.     

Phenotypic effects of overexpression of Agrobacterium rhizogenes T-DNA ORF13 in transgenic tobacco plants are mediated by diffusible factor(s)

Nicotiana tabacum cv. Xanthi transgenic plants expressing ORF13 of Agrobacterium rhizogenes 8196 T-DNA under the 35S RNA promoter from the cauliflower mosaic virus displayed developmental abnormalities. They were small, with short and variable internodal lengths, their root systems were poorly developed; leaves were small, asymmetric, rounded, wrinkled and dark green; flowers were short, and irregularly shaped. They exhibited reduced apical dominance and regularly produced offshoots at the base of the plant. This phenotype was also exhibited by offshoots of normal N. tabacum cv. Xanthi stock grafted with a transgenic scion indicating that expression of ORF13 influences plant development via diffusible factor(s).     

Mediation of pinocytosis in cultured arterial smooth muscle and endothelial cells by platelet-derived growth factor

Pinocytosis was measured in monkey aortic smooth muscle cells (SMC), bovine aortic endothelial cells, and Swiss 3T3 cells in culture as cellular uptake of [U-(14)C]sucrose and horseradish peroxidase (HRP) from the tissue culture medium. Monkey arterial SMC and Swiss 3T3 cells were maintained in a quiescent state of growth at low cells density in medium containing 5 percent monkey plasma-derived serum (PDS). Replacement of PDS with 5 percent monkey whole blood serum (WBS) from the same donor, or addition to PDS of partially purified platelet-derived growth factor(s) (PF), resulted in a marked stimulation of pinocytosis as well as of cellular proliferation. In SMC, enhancement of the rate of pinocytosis occurred 4-6 h after exposure to WBS or PF, and the rate was up to twofold higher than the rate in medium containing PDS. In contrast, [(3)H]thymidine uptake by SMC did not increase until 12-16 h after exposure to PF. In endothelial cells the presence of PF or WBS did not enhance either the rate of pinocytosis or the rate of proliferation over that in PDS. Thus, endothelial cells did not become quiescent at subconfluent densities in PDS but maintained rates of proliferation and pinocytosis that were equivalent to those in WBS. By autoradiography, the fraction of labeled nuclei in SMC cultures 24 h after change of medium increased from 0.061 +/- 0.004 in quiescent cultures to 0.313 +/- 0.028 after exposure to WBS or PF. In contrast, labeling indices of endothelial cells were similar for cultures grown in PDS, WBS, or PF at any single time point after change of medium. These findings suggest that the rate of pinocytosis maybe be coupled in some fashion to growth regulation, which may be mediated in part by specific growth factors, such as that derived from the thrombocyte.     

The number of vertebrate repeats can be regulated at yeast telomeres by Rap1-independent mechanisms

The number of telomeric DNA repeats at chromosome ends is maintained around a mean value by a dynamic balance between elongation and shortening. In particular, proteins binding along the duplex part of telomeric DNA set the number of repeats by progressively limiting telomere growth. The paradigm of this counting mechanism is the Rap1 protein in Saccharomyces cerevisiae. We demonstrate here that a Rap1-independent mechanism regulates the number of yeast telomeric repeats (TG(1-3)) and of vertebrate repeats (T(2)AG(3)) when TEL1, a yeast ortholog of the human gene encoding the ATM kinase, is inactivated. In addition, we show that a T(2)AG(3)-only telomere can be formed and maintained in humanized yeast cells carrying a template mutation of the gene encoding the telomerase RNA, which leads to the synthesis of vertebrate instead of yeast repeats. Genetic and biochemical evidences indicate that this telomere is regulated in a Rap1-independent manner, both in TEL1 and in tel1Delta humanized yeast cells. Altogether, these findings shed light on multiple repeat-counting mechanisms, which may share critical features between lower and higher eukaryotes.     

Control of stem cell fate by engineering their micro and nanoenvironment

Stem cells are capable of long-term self-renewal and differentiation into specialised cell types, making them an ideal candidate for a cell source for regenerative medicine. The control of stem cell fate has become a major area of interest in the field of regenerative medicine and therapeutic intervention. Conventional methods of chemically inducing stem cells into specific lineages is being challenged by the advances in biomaterial technology, with evidence highlighting that material properties are capable of driving stem cell fate. Materials are being designed to mimic the clues stem cells receive in their in vivo stem cell niche including topographical and chemical instructions. Nanotopographical clues that mimic the extracellular matrix(ECM) in vivo have shown to regulate stem cell differentiation. The delivery of ECM components on biomaterials in the form of short peptides sequences has also proved successful in directing stem cell lineage. Growth factors responsible for controlling stem cell fate in vivo have also been delivered via biomaterials to provide clues to determine stem cell differentiation. An alternative approach to guide stem cells fate is to provide genetic clues including delivering DNA plasmids and small interfering RNAs via scaffolds. This review, aims to provide an overview of the topographical, chemical and molecular clues that biomaterials can provide to guide stem cell fate. The promising features and challenges of such approaches will be highlighted, to provide directions for future advancements in this exciting area of stem cell translation for regenerative medicine.     

Genetic covariance between indices of body condition and immunocompetence in a passerine bird

Background  

Condition-dependence is a ubiquitous feature of animal life histories and has important implications for both natural and sexual selection. Mate choice, for instance, is typically based on condition-dependent signals. Theory predicts that one reason why condition-dependent signals may be special is that they allow females to scan for genes that confer high parasite resistance. Such explanations require a genetic link between immunocompetence and body condition, but existing evidence is limited to phenotypic associations. It remains unknown, therefore, whether females selecting males with good body condition simply obtain a healthy mate, or if they acquire genes for their offspring that confer high immunocompetence.     

Yeast diadenosine 5',5'-P1,P4-tetraphosphate alpha,beta-phosphorylase behaves as a dinucleoside tetraphosphate synthetase

The diadenosine 5',5'-P1,P4-tetraphosphate alpha,beta-phosphorylase (Ap4A phosphorylase), recently observed in yeast [Guaranowski, A., & Blanquet, S. (1985) J. Biol. Chem. 260, 3542-3547], is shown to be capable of catalyzing the synthesis of Ap4A from ATP + ADP, i.e., the reverse reaction of the phosphorolysis of Ap4A. The synthesis of Ap4A markedly depends on the presence of a divalent cation (Ca2+, Mn2+, or Mg2+). In vitro, the equilibrium constant K = ([Ap4A][Pi])/[(ATP][ADP]) is very sensitive to pH. Ap4A synthesis is favored at low pH, in agreement with the consumption of one to two protons when ATP + ADP are converted into Ap4A and phosphate. Optimal activity is found at pH 5.9. At pH 7.0 and in the presence of Ca2+, the Vm for Ap4A synthesis is 7.4 s-1 (37 degrees C). Ap4A phosphorylase is, therefore, a valuable candidate for the production of Ap4A in vivo. Ap4A phosphorylase is also capable of producing various Np4N' molecules from NTP and N'DP. The NTP site is specific for purine ribonucleotides (N = A, G), whereas the N'DP site has a broader specificity (N' = A, C, G, U, dA). This finding suggests that the Gp4N' nucleotides, as well as the Ap4N' ones, could occur in yeast cells.