Poly(pyrimidine) . poly(purine) synthetic DNAs containing 5-methylcytosine form stable triplexes at neutral pH

Poly(pyrimidine) . poly(purine) tracts have been discovered in the 5'-flanking regions of many eucaryotic genes. They may be involved in the regulation of expression since they can be mapped to the nuclease-sensitive sites of active chromatin. We have found that poly(pyrimidine) . poly(purine) DNAs which contain 5-methylcytosine (e.g. poly[d(Tm5C)] . poly[d(GA)]) will form a triplex at a pH below 8. In contrast, the unmethylated analogue, poly[d(TC)] . poly[d(GA)] only forms a triplex at pHs below 6. Synthetic DNAs containing repeating trinucleotides and poly[d(Um5C)] . poly[d(GA)] behave in a similar manner. Thus the stability of a triplex can be controlled by methylation of cytosine. This suggests a model for the regulation of expression based upon specific triplex formation on the 5'-side of eucaryotic genes.     

Sequence of an expressed human beta-tubulin gene containing ten Alu family members

The complete sequence of a functionally expressed human beta-tubulin gene (5 beta) is presented. The amino acid sequence encoded by this gene constitutes a distinct isotype, differing from a previously described human beta-tubulin sequence at 21 positions throughout the polypeptide chain. The beta-tubulin coding sequence in 5 beta is interrupted by three intervening sequences of 1014, 117 and 4826 nucleotides. The largest of these contains ten members of the Alu family of middle repetitive sequences. Together, these regions account for sixty percent of this intervening sequence. Two of the Alu elements are juxtaposed head to tail, and share the same flanking direct repeat. The ten Alu sequences are substantially divergent, both from each other and from an Alu consensus sequence, and several contain deletions of up to half the entire sequence.     

Bifunctional intercalation and sequence specificity in the binding of quinomycin and triostin antibiotics to deoxyribonucleic acid.

Quinomycin C, triostin A and triostin C are peptide antibiotics of the quinoxaline family, of which echinomycin (quinomycin A) is also a member. They all remove and reverse the supercoiling of closed circular duplex DNA from bacteriophage PM2 in the fashion characteristic of intercalating drugs, and the unwinding angle at I 0.01 is, in all cases, almost twice that of ethidium. Thus, as with echinomycin, they can be characterized as bifunctional intercalating agents. For the triostins this conclusion has been confirmed by measurements of changes in the viscosity of sonicated rod-like DNA fragments; the helix extension was found to be almost double that expected for a simple monofunctional intercalation process. For triostin A, further evidence for bifunctionality was derived from the cross-over point of binding isotherms to nicked circular and closed circular bacteriophage-PM2DNA. Binding curves for the interaction of quinomycin C and triostin A with a variety of synthetic and naturally occurring nucleic acids were determined by solvent-partition analysis, but triostin C was too insoluble in aqueous solution to make this method applicable. For quinomycin C the highest binding constant was found with Micrococcus lysodeikticus DNA, and its pattern of specificity among natural DNA species was broadly similar to that of echinomycin, although the binding constants were 2--6 times as large. For triostin A the highest binding constant was again found for M. lysodeikticus DNA, but the specificity pattern was quite different from that of the quinomycins. In particular, triostin A bound better to poly(dA-dT) than to the poly(dG-dC) whereas this order was reversed for quinomycin C. There was also evidence that the binding to poly(dA-dT) might be co-operative in nature. No significant interaction could be detected with poly(dA).poly(dT) or with RNA from Escherichia coli. Poly(dG).poly(dC) gave variable results, depending on the source of the polymer. The different patterns of specificity displayed by the quinomycins and triostins are tentatively ascribed to differences in their conformations in solution.     

Integument and sensory nerve differentiation ofDrosophila leg and wing imaginal discs in vitro

Summary An ultrastructural analysis is presented of the cuticular and neural structures formed by the prothoracic leg and wing imaginal discs of maleDrosophila melanogaster larvae during culture in vitro with 0.2 g/ml of -ecdysone. A pupal cuticle, and subsequently an imaginal cuticle with a well-defined epicuticle and a laminated endocuticle is formed. The ultrastructure of the epidermis and of cuticular structures such as bristles, trichomes, apodemes, and tracheoles is very similar to that found in situ. Dendrites and nerve cell bodies are formed in vitro, and sensory axons form nerve bundles similar to those of normal appendages in situ, despite their isolation from the central nervous system. It is concluded that at the ultrastructural level, differentiation in vitro closely parallels the normal course of development.     

Arachidonic acid metabolism in rat basophilic leukemia (RBL-1) cells

Rat basophilic leukemia (RBL-1) cells metabolized arachidonic acid through more than one enzymatic pathway. The major cyclooxygenase product was prostaglandin (PG) D₂ as established by chromatographic and chemical behavior and the effect on platelet aggregation. PGD₂ formation from exogenous arachidonic acid was inhibited by indomethacin, 1 μg/ml. RBL-1 incubated with exogenous arachidonic acid also formed SRS-A the synthesis of which was not inhibited by indomethacin. However, the SRS-A activity was blocked by the specific receptor antagonist FPL 55712. [¹⁴C]arachidonic acid was effectively incorporated into the phospholipids of RBL-1 cells. Challenge of such prelabelled cells or unlabelled cells with A 23187 caused release of PGD₂, SRS-A and another presently unidentified product. However, with A 23187 as a stimulus, the RBL-1 cyclo-oxygenase could not be blocked by low concentrations of indomethacin. This work further substantiates our earlier findings that SRS-A formed from arachidontic acid is not a cyclooxegenase product.     

Third system for neutral amino acid transport in a marine pseudomonad.

Uptake of leucine by the marine pseudomonad B-16 is an energy-dependent, concentrative process. Respiratory inhibitors, uncouplers, and sulfhydryl reagents block transport. The uptake of leucine is Na+ dependent, although the relationship between the rate of leucine uptake and Na+ concentration depends, to some extent, on the ionic strength of the suspending assay medium and the manner in which cells are washed prior to assay. Leucine transport can be separated into at least two systems: a low-affinity system with an apparent Km of 1.3 X 10(-5) M, and a high-affinity system with an apparent Km of 1.9 X 10(-7) M. The high-affinity system shows a specificity unusual for bacterial systems in that both aromatic and aliphatic amino acids inhibit leucine transport, provided that they have hydrophobic side chains of a length greater than that of two carbon atoms. The system exhibits strict stereospecificity for the L form. Phenylalanine inhibition was investigated in more detail. The Ki for inhibition of leucine transport by phenylalanine is about 1.4 X 10(-7) M. Phenylalanine itself is transported by an energy-dependent process whose specificity is the same as the high-affinity leucine transport system, as is expected if both amino acids share the same transport system. Studies with protoplasts indicate that a periplasmic binding protein is not an essential part of this transport system. Fein and MacLeod (J. Bacteriol. 124:1177-1190, 1975) reported two neutral amino acid transport systems in strain B-16: the DAG system, serving glycine, D-alanine, D-serine, and alpha-aminoisobutyric acid; and the LIV system, serving L-leucine, L-isoleucine, L-valine, and L-alanine. The high-affinity system reported here is a third neutral amino acid transport system in this marine pseudomonad. We propose the name "LIV-II" system.     

CALCIUM ION DEPENDENCE OF THE 2-SITE IMMUNORADIOMETRIC ASSAY OF MOORE''S S-100 PROTEIN

Abstract— The two-site immunoradiometric assay (two-site IRMA) for a specific protein of the nervous system, S-100, is carried out by reaction of the S-100 protein solution with a solid-phase anti(S-100) followed by a second reaction in which the insoluble product is incubated with purified, radioactive anti(S-100). Unreacted labeled antibodies remain in solution and are washed away. As the amount of S-100 increases, the radioactivity in the solid-phase increases. The most significant assay variable is the effect of calcium on the assay dose-response. 0.1 mM-EDTA causes a total inhibition of the dose-response curve which is reversed by increasing the concentration of calcium ions. The dose-response reaches a maximum at 1.0mM-Ca²⁺. then becomes progressively inhibited as the Ca²⁺ concentration is increased further. Previous immunochemical studies of S-100 which did not allow for this effect must now be interpreted with caution.