The rep region of pR plasmid regulates the expression of SOS system

Summary By using an artificial hybrid between phage and the pR plasmid, we have shown that the rep region of the pR plasmid encodes a function which regulates the expression of the muc genes (plasmid genes that are under the negative control of lexA and responsible for an increased rate of spontaneous mutagenesis and resistance to UV and chemicals). Expression of the muc genes was monitored by a fusion between the muc promoter and the lacZ structural gene. When E. coli cells containing such a fusion are infected by the hybrid pR phasmid, -galactosidase activity is enhanced, indicating that pR encodes an antagonist of lexA. By deletion mapping we have located the gene encoding the antagonist of lexA (bat) in the rep region of the plasmid. The bat gene product can also antagonize the cI repressor as shown by the observation that pR phasmids are virulent on a homoimmune lysogen. We have exploited this latter property to carry out genetic and functional analysis of the bat region. This region is organized as a classical operon where the expression of the bat structural gene is negatively regulated by a repressor gene that encodes a proteic product.     

A physico-chemical approach to the study of the binding interaction between S-adenosyl-L-methionine and polyanions: binding constants and nature of the interaction with sodium poly(styrene sulfonate)

The interaction between S-adenosyl-L-methionine (AdoMet) and sodium poly(styrene sulfonate) NaPSS) was studied by means of ultrafiltration and ultraviolet absorption spectroscopy at several pH values and sodium sulfate concentrations. The results obtained are interpreted mainly in terms of electrostatic interactions and permit the evaluation of the binding constants under different experimental conditions. Furthermore, ultraviolet absorption spectroscopy data show a specific short-range interaction between the aromatic electronic system of AdoMet and the NaPSS aromatic ring. The results indicate that the binding strength is greatly affected by the AdoMet positive charge on the adenine ring. The other positive charges on both the sulfonic pole and the amino acidic group of AdoMet contribute only weakly to the binding to the polyanionic matrix, thus assuring some stability of AdoMet even at physiological pH.     

Mono and two-dimensional 500-MHz characterization of synthetic bombesin and related peptides in DMSO and DMSO-water

The proton nmr characterization of bombesin (BBS) and of two peptide fragments corresponding to the (1-6) and (6-14) sequences has been carried out at 500 MHz in dimethyl sulfoxide (DMSO-d6) using two-dimensional (2D) homo and 1H-13C heterocorrelated techniques. All resonances in the nmr spectra have been assigned and several coupling constants have been measured. The backbone J alpha CH-NH coupling constants are quite similar and around 7.8-8.2 Hz, pointing to an unfolded structure in DMSO-d6. The possibility of secondary structures in highly viscous mixtures of DMSO-d6-water was investigated. The existence of sequential nuclear Overhauser enhancement (NOE) effects in the C-terminal nonapeptide section may indicate a preferential site for secondary structuring.     

Bicyclic peptides: solution conformation and Ca2+ binding of the heterodetic bicyclic decapeptide cyclo(Glu1-Leu2-Pro3-Gly4-Ser5-Ile6-Pro7-Ala8)- cyclo(1 gamma----5 beta)Phe9-Gly10

The conformational behavior of a heterodetic bicyclic decapeptide (BCPLT) in the absence and in the presence of calcium ions has been studied by means of mono and two-dimensional nmr techniques. Free BCPLT possesses a quite compact structure stabilized by intramolecular bonds and turns. In the structure a cluster of carbonyls is located in a cavity that is supposed to be the cation binding site.     

Voltage-dependent channels permeable to K+ and Na+ in the membrane ofAcer pseudoplatanus vacuoles

Summary The patch-clamp technique in whole-cell configuration was used to study the electrical properties of the tonoplast in isolated vacuoles fromAcer pseudoplatanus cultured cells. In symmetrical KCl or K₂ malate solutions, voltage- and time-dependent inward currents were elicited by hyperpolarizing the tonoplast (inside negative), while in the positive range of potential the conductance was very small. The specific conductance of the tonoplast at –100 mV, in 100mm symmetrical KCl was about 160 S/cm². The reversal potentials (E _rev) of the current, measured in symmetrical or asymmetrical ion concentrations (cation, anion or both) were very close to the values of the K⁺ equilibrium potential. Experiments performed in symmetrical or asymmetrical NaCl indicate that Na⁺ too can flow through the channels. NeitherE _rev nor amplitude and kinetics of the current changed by replacing NaCl with KCl in the external solution. These results indicate the presence of hyperpolarization-activated channels in tonoplasts, which are permeable to K⁺ as well as to Na⁺. Anions such as Cl^– or malate seem to contribute little to the channel current.     

Tricyclic Imipramine Modification of the Circadian Rhythms of Hypothalamic Serotonin, its Precursors and Acid Catabolite in Individually Housed Rats

Circadian rhythms of serotonin (5HT), its precursors tryptophan (TP) and 5-hydroxy-tryptophan (5HTP) and its acid catabolite 5-hydroxy-indoleacetic acid (5HIAA), were determined in the hypothalamus of control rats and rats which had been treated continuously with subcutaneous imipramine (10 mg/kg/day) for 2 weeks.

Rats were individually housed and entrained to LD12:12. Controls showed the 5HT and TP peaks in the light and dark periods respectively, as reported in the literature, but no inverted correlation (antiphase) between SHT and 5HIAA rhythms.

Imipramine significantly modified circadian rhythm characteristics: the 5HT acrophase was advanced, that of TP and 5HIAA was delayed. Imipramine also significantly increased hypothalamic SHT and TP concentrations.