We have investigated the capacity of N- and C-terminally truncated and chimeric human (h) IgE-derived peptides to inhibit the binding of 125I-labeled hIgE, and to engage cell lines expressing high and low affinity receptors (Fc-epsilon-RI/II). The peptide sequence Pro343-Ser353 of the hC-epsilon-3 domain is common to all h-epsilon-chain peptides that recognize hFc-epsilon-RI. This region in IgE is homologous to the A loop in C-gamma-2 that engages the rat neonatal IgG receptor. Optimum Fc-epsilon-RI occupancy by hIgE occurs at pH 6.4, with a second peak at 7.4. N- or C-terminal truncation has little effect on the association rate of the ligands with this receptor. Dissociation markedly increases following C-terminal deletion, and hFc-epsilon-RI occupancy at pH 6.4 is diminished. His residue(s) in the C-terminal region of the epsilon-chain may thus contribute to the high affinity of interaction. Grafting the homologus rat epsilon-chain sequence into hIgE maintains hFc-epsilon-RI interaction without conferring binding to rat Fc-epsilon-RI. hFc-epsilon-RII interaction is lost, suggesting that these residues also contribute to hFc-epsilon RII binding. h-epsilon-chain peptides comprising only this sequence do not block hIgE/hFc-epsilon-RI interaction or engage the receptor. Therefore, sequences N- or C-terminal to this core peptide provide structures necessary for receptor recognition.

Background: The multimeric DNA-dependent RNA polymerases are widespread throughout nature. The RNA polymerase of Escherichia coli, which is the most well characterized, consists of a holoenzyme with subunit stoichiometry of ␣ 2 ␤␤ 0 . The ␤ subunit is conserved and has been implicated in all stages of transcription. The extreme C-terminus of the ␤ subunit, which includes two well-conserved sequence segments, contributes to the active centre and has been proposed to act in transcriptional termination. We describe a genetic system for further characterizing the role of the extreme Cterminus of the ␤ subunit of E. coli RNA polymerase. This involves random, PCR (Polymerase Chain Reaction)-mediated mutagenesis of the 3 0 region of rpoB encoding the C-terminal 116 amino acids of ␤, followed by the isolation and characterization of trans-dominant-negative mutations.

No abstract

Locally available bentonite clay has been modified by magnesium and used to eliminate acid blue 129 from aqueous solutions. The adsorption was studied under different experimental conditions such as dye concentrations, temperature, and shaking time. The adsorption of the dye increased with time and followed the pseudo-first-order kinetic with rate constant "k" 0.126 min -1 at 283 K. Thermodynamic parameters such as ΔH°, ΔS°, and ΔG° were calculated from the slope and intercept of the linear plots of ln K against 1/T. Analysis of adsorption results obtained at temperatures of 283, 293, 303, and 313 K showed that the adsorption pattern on bentonite seems to follow Langmuir and Freundlih. The increase in temperature reduces adsorption capacity by magnesium-modified bentonite due to the enhancement of the desorption step in the mechanism. The activation energy of the adsorption process was found to be 3.55 kJ mol -1 . The Mg-bentonite showed better adsorption than Ba and Al-bentonite. Our study reveals that abundantly available local clay may be used to eliminate dyes from aqueous solutions.

No abstract