Continuous synthesis of the dnaA gene product of Escherichia coli in the cell cycle

Summary The dnaA gene product of Escherichia coli, identified as a weakly basic protein of about 48,000 daltons (Yuasa and Sakakibara 1980), can be separated from other celluar proteins by means of two-dimensional gel electrophoresis. Synthesis of the dnaA protein took place continuously during a cell growth cycle. The newly synthesized dnaA protein persisted stably for one generation. Thermosensitive dnaA protein produced by the dnaA167 mutant was stable at 30° C, but was disintegrated at 42° C. The amount of intact dnaA protein present in the mutant exposed to the high temperature for 60 min was less than a quarter of the amount at the time of the shift. The cells having the reduced amount of intact dnaA protein were capable of initiating a new round of chromosome replication at the low temperature without de novo synthesis of the dnaA protein. The potential of the mutant for initiation of DNA replication decreased with reduction in the amount of the thermoreversible dnaA protein. The mutations dnaA167 and dnaA46 had no significant effect on the syntheses of the dnaA mRNA and the protein product at the low and high temperatures.Abbreviations used SDS sodium dodecyl sulfate - kb kilobase pairs - TCA trichloroacetic acid     

Participation and Properties of Lipoxygenase and Hydroperoxide Lyase in Volatile C6-Aldehyde Formation from C18-Unsaturated. Fatty Acids in Isolated Tea Chloroplasts

Isolated tea chloroplasts utilized linoleic acid, linolenicacid and their 13-hydroperoxides as substrates for volatileC₆-aldehyde formation. Optimal pH values for oxygen uptake,hydroperoxide lyase and the overall reaction from C₁₈-fattyacids to C₆-aldehydes were 6.3, 7.0 and 6.3, respectively. Methyllinoleate, linoleyl alcohol and -linolenic acid were poor substratesfor the overall reaction, but linoleic and linolenic acids weregood substrates. The 13-hydroperoxides of the above fatty acidsand alcohol also showed substrate specificity similar to thatof fatty acids. Oxygen uptakes (relative V_max) with methyl linoleate,linoleyl alcohol, linolenic acid, -linolenic acid and arachidonicacid were comparable to or higher than that with linoleic acid.In winter leaves, the activity for C₆-aldehyde formation fromC₁₈-fatty acids was raduced to almost zero. This was due tothe reduction in oxygenation. The findings presented here provideevidence for the involvement of lipoxygenase and hydroperoxidelyase in C₆-aldehyde formation in isolated chloroplasts. (Received July 11, 1981; Accepted November 5, 1981)     

Guest-induced conformational change of β-cyclodextrin capped with an environmentally sensitive chromophore

A capped cyclodextrin, 6-deoxy-6-(p-hydroxy-m-nitrophenacylthio)-β-cyclodextrin, was prepared in order to detect any conformational change of the host upon the guest binding. The association constant between the cyclodextrin and 1-adamantanecarboxylate, cyclohexanecarboxylate, p-methylbenzoate, 3,3-dimethylbutyrate, or 2,2-dimethylpropionate was enhanced 20, 5.3, 3.7, 2.3, or 2.0 times, respectively, by chromophore capping. The changes in the electronic, NMR, and circular dichroism spectra as well as pK_a of this cyclodextrin upon binding of the guest strongly indicate a conformational change around the chromophoric moiety of the cyclodextrin.     

Presence of dynorphin-like immunoreactivity in rat pituitary gland and hypothalamus

Using a highly specific and sensitive radioimmunoassay for dynorphin(1-13), dynorphin-like immunoreactivity (dynorphin-LI) was detected in rat pituitary and hypothalamus. Gel chromatographic studies on Sephadex G-50 revealed three components of dynorphin-LI with molecular weights of approximately 7500-9500 (big dynorphin), 3500-5500 (intermediate dynorphin) and 1600-1900 (small dynorphin), the latter of which eluted at the same position as authentic dynorphin contamination in porcine ACTH extracts (Sigma). Dynorphin-LI in rat anterior pituitary existed mainly as big dynorphin, whereas dynorphin-LI in rat intermediate-posterior pituitary and hypothalamus eluted mainly at the position of authentic small dynorphin.     

Rat cathepsin H-catalyzed transacylation: comparisons of the mechanism and the specificity with papain-superfamily proteases.

We found that rat cathepsin H showed strong transacylation activity under physiological conditions. It is a feature of cathepsin H to utilize amino acid amides not only as acyl-acceptors but also as acyl-donors in the reaction. The pH-dependence of the transacylation activity was distinct from those of other papain-superfamily proteases. The alkaline limb (pKapp = 7.5) could be regarded as the pKa of the alpha-amino group of the acyl-donor, which was also involved in the original amino-peptidase activity. The acidic limb (pKapp = 5.8) was suggested to be involved in the deacylation step, where amino acid amide attacked the acyl-intermediate as a nucleophile in place of water in the hydrolysis. Although the N alpha-deprotonated acyl-acceptor, which is supposed to govern the nucleophilic attack, has a small population in the acidic pH range (above pH5), the transacylation was detectable even at the acidic pH-range because of the high S1'-site binding ability and suitable nucleophilicity of the acyl-acceptor. In the transacylation between various amino acid amides, the S1 and S1' site appeared to prefer hydrophobic residues without and regardless of a branch at beta-carbon, respectively. From these results and the sequence homology in the papain superfamily, we concluded that the reaction was governed by the acyl-donor having a protonated amino group, the acyl-acceptor having a deprotonated amino group and the remarkable hydrophobic character (especially favoring tryptophan amide) of the S1' site, presumably reflecting the good conservation of Trp177 in papain-superfamily proteases.     

Preparation and properties of a lysozyme derivative in which two domains are cross-linked intramolecularly between Trp62 and Asp101.

A lysozyme derivative in which two domains were cross-linked intramolecularly was newly prepared by means of a two-step reaction. First, the beta-carboxyl group of Asp101 in lysozyme was selectively modified with 2-(2-pyridyldithio)ethylamine in the presence of 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide hydrochloride. After reduction of the pyridyldithio moiety of Asp101 modified lysozyme at pH 4.5 with dithiothreitol, the derivative was allowed to cross-link intramolecularly by reaction with 1,3-dichloroacetone at pH 7. Intramolecularly cross-linked lysozyme thus formed was purified by gel chromatography followed by ion-exchange chromatography. Based on the results of 1H-NMR and peptide analyses, it was concluded that Asp101 was cross-linked to Trp62 with a -CH2COCH2SCH2CH2NH-bridge in this derivative. The derivative showed minor but distinct activity against Micrococcus lysodeikticus and glycol chitin. Its melting temperature for thermal denaturation was higher by 7.3 degrees than that of native lysozyme at pH 3.     

A ring of uncharged polar amino acids as a component of channel constriction in the nicotinic acetylcholine receptor.

The channel pore of the nicotinic acetylcholine receptor (AChR) has been investigated by analysing single-channel conductances of systematically mutated Torpedo receptors expressed in Xenopus oocytes. The mutations mainly alter the size and polarity of uncharged polar amino acid residues of the acetylcholine receptor subunits positioned between the cytoplasmic ring and the extracellular ring. From the results obtained, we conclude that a ring of uncharged polar residues comprising threonine 244 of the alpha-subunit (alpha T244), beta S250, gamma T253 and delta S258 (referred to as the central ring) and the anionic intermediate ring, which are adjacent to each other in the assumed alpha-helical configuration of the M2-containing transmembrane segment, together form a narrow channel constriction of short length, located close to the cytoplasmic side of the membrane. Our results also suggest that individual subunits, particularly the gamma-subunit, are asymmetrically positioned at the channel constriction.     

Inhibition of epidermal growth factor-induced DNA synthesis by tyrosine kinase inhibitors

We prepared methyl 2,5-dihydroxycinnamate as a stable analogue of erbstatin, a tyrosine kinase inhibitor. This analogue was about 4 times more stable than erbstatin in calf serum. It inhibited epidermal growth factor receptor-associated tyrosine kinase in vitro with an IC₅₀ of 0.15 μg/ml. It also inhibited in situ autophosphorylation of epidermal growth factor receptor in A431 cells. Methyl 2,5-dihydroxycinnamate was shown to delay the S-phase induction by epidermal growth factor in quiescent normal rat kidney cells, without affecting the total amount ofDNA synthesis. The effect of erbstatin on S-phase induction was smaller, possibly because of its shorter life time.