The Gene Encoding Flavanone 3-Hydroxylase is Expressed Normally in the Pale Yellow Flowers of the Japanese Morning Glory Carrying the speckled Mutation Which Produce Neither Flavonol nor Anthocyanin but Accumulate Chalcone, Aurone and Flavanone

The Japanese morning glory carrying the recessive mutable speckledallele with the dominant speckled-activator bears colorlessflowers with fine and round colored spots distributed over thecorolla whereas the plant without the speckled-activator producespale yellow flowers. Previous chemical analysis has indicatedthat a mutation in the gene for flavanone 3-hydroxylase (F3H)is a likely candidate for the speckled allele. However, theF3HmRNA without sequence alteration accumulates normally inthe pale yellow flowers, indicating that the speckled alleleis neither the F3H gene nor a regulatory gene acting on theF3H gene expression. (Received April 4, 1997; Accepted June 2, 1997)     

petR, located upstream of the fbcFBC operon encoding the cytochrome bc1 complex, is homologous to bacterial response regulators and necessary for photosynthetic and respiratory growth of Rhodobacter capsulatus

Interposon mutagenesis of a region upstream of the petABC(fbcFBC) operon, encoding the ubiquinol: cytochrome c2 oxidoreductase (bc1 complex) of the photosynthetic bacterium Rhodobacter capsulatus revealed the presence of two genes, petP and petR. DNA nucleotide sequence determination of this region indicated that petP and petR are transcribed in the same direction as the petABC(fbcFBC) operon, and are translationally coupled. A silent insertion located in the interoperonal region separating petPR and the petABC(fbcFBC) genes indicated that these clusters have separate promoters. The deduced amino acid sequence of the putative petR gene product is homologous to various bacterial response regulators, especially to those of the OmpR subgroup. Moreover, it was found that PetR mutants are unable to grow on rich or minimal media by either photosynthesis or respiration, demonstrating that these gene products are essential for growth of R. capsulatus.     

Evidence for Structural Dissimilarity in the Neurotransmitter Binding Region of Purified Acetylcholine Receptors from Human Muscle and Torpedo Electric Organ

Acetylcholine receptor (AChR) purified from human skeletal muscle affinity-alkylated with bromoacetyl[methyl-3H]choline bromide ([3H]BAC) in mildly reducing conditions to yield a specifically radiolabeled polypeptide, Mr 44,000, the alpha-subunit. The binding of [125I]alpha-bungarotoxin to AChR was completely inhibited by affinity-alkylation, indicating that the human AChR's binding site for alpha-bungarotoxin is closely associated with the alpha-subunit's acetylcholine binding site. Structures in the vicinity of the alpha-bungarotoxin binding sites of AChRs from human muscle and Torpedo electric organ were compared by varying the conditions of alkylation. Under optimal conditions of reduction and alkylation, both human and Torpedo AChR incorporated BAC in equivalence to the number of alpha-bungarotoxin binding sites. However, with limited conditions of reduction but sufficient BAC to alkylate 100% of the alpha-bungarotoxin binding sites of human AChR, only 71% of the Torpedo AChR's binding sites were alkylated. In optimal conditions of reduction but with the minimal concentration of BAC that permitted 100% alkylation of the human AChR's alpha-bungarotoxin sites, only 74% of the Torpedo AChR's binding sites were alkylated. These data suggest that the neurotransmitter binding region of human muscle AChR is structurally dissimilar from that of Torpedo electric organ, having a higher binding affinity for BAC and an adjacent disulfide bond that is more readily accessible to reducing agents.     

Analytical studies on the responses of sunflower (Helianthus annuus) to various defoliation treatments

The effects of defoliation treatments on plant growth in sunflower (Helianthus annuus) were studied in the field. Four defoliation treatments, 0 (control), 37.4, 56.1 and 93.4% of the total leaf dry weight, were applied to plants that had small third leaves. Decreased leaf weight/whole plant weight (F/W) ratios in defoliated plants rapidly recovered to almost the same ratio as that observed in the control within 12 to 16 days after defoliation according to the degree of defoliation. The mechanism involved in the recovery of the F/W ratio in defoliated plants mainly consisted of three parameters: enhancement of (1) carbon distribution ratios in the leaves, (2) photosynthetic activity in the remaining leaves, and (3) retranslocation of carbon from the stem and/or roots to leaves. Inhibitive effects of defoliation on relative growth rate and net assimilation rate were seen at an early stage, but subsequently both rates became larger in defoliated plants than in controls. Defoliated plants tended to show rapid development and expansion of new leaves, and to show increased specific leaf area and protein synthesis in individual leaves. The sugar content of leaves in defoliated plants was higher than that in controls, while the content in both stem and roots was lower. These responses seem to be advantageous for development of the photosynthetic system. Heights of defoliated plants were clearly depressed according to the degree of defoliation, and this was attributed largely to differences in the elongation rates of the internodes resulting from defoliation.     

Phospholipase C in human endometrial fibroblasts and its regulation by estrogens

1. Stimulated inositolphospholipid turnover has been proposed as a signal-transducing mechanism in many cell types. It appears to be initiated by stimulation of hydrolysis of inositolphospholipid by a phospholipase C. 2. In human endometrial fibroblasts, estradiol was observed to cause sequential enhancement of [32P]phosphate incorporation into phosphatidic acid (PA) and phosphatidylinositol (PI), indicating an accelerating effect of estradiol on inositolphospholipid turnover. Specific 32P-radioactivity in the gamma-phosphate of ATP was increased in response to estradiol. Estrone or estriol were without any effects. 3. To investigate possible mechanisms by which estradiol activates a phospholipase C enzyme in the fibroblasts, the plasma membrane fraction isolated from the fibroblasts was exposed to estradiol in the presence of guanosine triphosphate (GTP) to detect inositol trisphosphate (IP3) production. The IP3 production was Ca2+ dependent, a dependency not affected by estradiol. 4. However, ATP decreased the Ca2+ concentration required for IP3 production in a dose-dependent manner; adenosine diphosphate (ADP), cytidine triphosphate (CTP) showed no effects. 5. These findings from cell and cell-free systems might suggest that estradiol stimulates a phospholipase C, as a result of enhancement of intracellular ATP synthesis, but not as a result of a direct effect on the enzyme molecule or direct activation of receptor-phospholipase C unit. 6. This may give us new insight into estrogen-stimulated cellular phenomenon through some mechanisms other than that classically associated with the action of estrogen.     

Identification of N-[p-(2-benzimidazolyl)phenyl]maleimide-modified residue participating in dynamic fluorescence changes accompanying Na+,K+-dependent ATP hydrolysis

Na+,K+-ATPase from pig kidney was specifically modified with a sulfhydryl fluorescent reagent, N-[p-(2-benzimidazolyl)phenyl]maleimide (BIPM), by pretreatment of N-ethylmaleimide. The preparation thus obtained retained 100% of initial Na+,K+-ATPase activity and contained 1 BIPM residue/alpha-chain, and it showed almost 2-fold larger fluorescence changes accompanying ATP hydrolysis than the previous preparations which retained 60% of initial activity and contained 3-4 BIPM residues/alpha-chain (Taniguchi, K., Suzuki, K., and Iida, S. (1982) J. Biol. Chem. 257, 10659-10667). Extensive trypsin (Sigma type I) treatment of the new preparation produced mainly two different fluorescent peptide peaks in both ion-exchange and reverse-phase chromatography. Amino acid sequence analysis of both peptides showed that they had the same common sequence, Ser-Tyr-X-Pro-Gly-Met-Gly-Val, except that the larger one contained Ala-Leu next to the Val residue. From the comparison of the amino acid sequence deduced from cDNA from sheep kidney (Shull, G. E., Schwartz, A., and Lingrel, J. B. (1985) Nature 316, 691-695), X was shown to correspond to Cys-964 of the alpha-chain in Na+,K+-ATPase. The data suggest that the microenvironment of the BIPM residue covalently bound to the sulfhydryl group of Cys-964 changes accompanying sequential appearance of reaction intermediates of Na+,K+-ATPase.     

Bacteriophage P1 derivatives unaffected in their growth by a large inversion or by IS insertions at various locations

Several plaque-forming phage P1 derivatives carrying DNA rearrangements associated with IS elements are described. They have IS1, IS3 and IS5 inserted in four distinct locations, all of which are non-essential regions for phage P1 propagation. One derivative carries a genome segment, inverted relative to the one in the P1 wild-type genome, between two inverted copies of IS1. The inverted DNA segment spans about 23 kb of the 90 kb long P1 genome and it includes the invertible C segment. This phage is as viable as an isomeric P1 which carries the relevant segment in its original orientation. These results are discussed with regard to the genome organization of phage P1.