Replication of Fpoh+ plasmid in mafA mutants of Escherichia coli defective in plasmid maintenance

Summary A class of F plasmids, designated Fpoh ⁺, was previously shown to be able to replicate extrachromosomally on Hfr strains by virtue of carrying the specific site or region poh ⁺ (permissive on Hfr) of the E. coli chromosome (Hiraga, 1975, 1976a). These plasmids were now found to replicate on E. coli mafA mutants (mafA1 and mafA23) that cannot support vegetative replication of F and some other F-like plasmids. The derivatives of Fpoh ⁺ that have lost the poh ⁺ site, on the other hand, failed to replicate on mafA mutants. These mutants harboring Fpoh ⁺ (but not Poh^- derivatives thereof) exhibit abnormal cell division and form elongated cells, presumably due to competition between Fpoh ⁺ and the host chromosome for some factor(s) essential for the initiation of DNA replication of the both replicons. It is tentatively concluded that the poh ⁺ site is required for F plasmids to replicate on mafA mutants as well as on Hfr strains. In view of the fact that the mechanism of inhibition of autonomous F DNA replication in mafA mutants and in Hfr strains are clearly different, the present data seem to provide strong support to the notion that the poh ⁺ region contains the replication origin of the E. coli chromosome.     

Photosynthetic activities of a thermophilic blue-green alga

Photosynthetic activities of a thermophilic blue-green alga,a species of Synechococcus, were studied with special referenceto its growth at high temperatures. A rapid algal growth occurredin the temperature range between 50 and 60?C, showing the maximumrate, six doublings per day, at about 57?C. Photosynthetic oxygenevolution and methyl viologen photoreduction in the cells werealso active at high temperatures and the optimum temperaturesfor these activities agreed with that of the algal growth. Thegrowth and photosynthetic activities were very low at room temperatureand irreversibly inactivated at temperatures above 60?C. The thylakoid membranes isolated from the alga were also photochemicallyactive at high temperatures. The membranes mediated ferricyanidephotoreduction coupled with a stoichiometric oxygen evolutionat a rate comparable to that of photosynthetic oxygen evolutionin the cells. The optimum temperature for the reaction was ashigh as 50?C. The membranes also showed a photosystem I-mediatedreaction at high temperatures. These observations indicate thatthe thylakoid membranes are intrinsically thermophilic in thisorganism. Thus the growth of the alga at high temperatures canbe well correlated to thermophilic properties of the photosyntheticapparatus. (Received February 20, 1978; )     

Synthetic gibberellin synergists in elongation of shoot growth ofOryza sativa L.

Previous studies showed that 2-ethyl-3-methoxycarbonyl-1-(p-tolylcarbamoyl) isourea acts as a potent GA₃-synergist in stimulating shoot growth of rice seedlings. Studies with several structurally related compounds show that the alkoxycarbonylcarbamoyl-isourea or -isothiourea skeleton is required for biological activity. Any chemical deletion from this skeleton causes complete loss of activity. From present and previous data it seems that alkoxycarbonylcarbamoyl-isourea or -isothiourea is converted by intramolecular cyclization in the rice seedlings into the corresponding triazinone that serves as the active form.Part 9 in the series Plant Growth-regulating Activities of Isourea Derivatives and Related Compounds; for Part 8 seeReferences, Ogawa et al. (1980b)     

Synthetic gibberellin synergists in elongation of shoot growth ofOryza sativa L.

Previous studies showed that 2-ethyl-3-methoxycarbonyl-1-(p-tolylcarbamoyl) isourea acts as a potent GA₃-synergist in stimulating shoot growth of rice seedlings. Studies with several structurally related compounds show that the alkoxycarbonylcarbamoyl-isourea or -isothiourea skeleton is required for biological activity. Any chemical deletion from this skeleton causes complete loss of activity. From present and previous data it seems that alkoxycarbonylcarbamoyl-isourea or -isothiourea is converted by intramolecular cyclization in the rice seedlings into the corresponding triazinone that serves as the active form.     

Induction of histidine decarboxylase activity in mouse skin after application of indole alkaloids,a new class of tumor promoter

The effects of various promoters in two-step carcinogenesis on the induction of histidine decarboxylase in the skin of mice was investigated. The potencies of various phorbol esters in inducing histidine decarboxylase activity were parallel with their tumor-promoting activities. Indole alkaloids such as dihydroteleocidin B and lyngbyatoxin A, which induced ornithine decarboxylase and promoted tumor development in the skin of mice with the same potency as 12-O-tetradecanoylphorbol-13-acetate (TPA), also induced histidine decarboxylase activity. These results suggest that histamine produced by this inducible histidine decarboxylase may play some role in tumor promotion.     

Changes in Electrophoretic Patterns of Oocyte Proteins during Oocyte Maturation in Oryzias latipes

Changes in the two-dimensional SDS-electrophoretic patterns of extracts of maturing denuded oocytes of the medaka ( Oryzias latipes ) were surveyed. In oocytes without follicular constituents several proteins became detectable in the area between the acidic and slightly basic proteins on the two-dimensional electrophoretograms, while a few of the protein spots disappeared during the process of oocyte maturation. The former proteins were detected also in oocytes that were induced to mature in vivo without breakdown of the germinal vesicle. Several proteins newly observed in extracts of post-vitellogenic oocytes during maturation after breakdown of the germinal vesicle were also identified by two-dimensional electrophoresis. Of several proteins that exhibited noticeable changes in maturing oocytes, only one spot incorporated ¹⁴C-labeled amino acid during maturation, suggesting that post-translational modification of many proteins occurred during oocyte maturation.     

Development of the Formula-Detoxification System during Adaptation to Air of Submerged Rice Seedlings

Changes in activities of enzymes and levels of antioxidant substratesinvolved in the -detoxification system in seedlings of rice (Oryza sativa L. cv. Yamabiko) inresponse to variations in the oxygen environment were studied.Activities of superoxide dismutase, ascorbate peroxidase, monodehydroascorbatereductase, dehydroascorbate reductase, glutathione reductaseand catalase, expressed either on the basis of fresh weightof shoots or relative to levels of soluble protein were muchlower in seedlings germinated under water for 6 days than inthose germinated in air for the same period of time. When submergedseedlings were exposed to air, the activities of these six enzymesincreased to or exceeded the levels in aerobically grown controlsduring 24 h of adaptation to air. Ascorbate and glutathione,which act as antioxidant substrates in the -detoxification system, were present in submergedseedlings at nearly the same levels as those found in aerobicallygrown controls. On exposure of submerged seedlings to air, thelevel of ascorbate in creased slightly, but the level of glutathioneshowed a rapid increase, reaching 7 times that in aerobicallygrown controls within 12 h of adaptation to air. Levels of allsix antioxidative enzymes and of two substrates involved inthe detoxification of the superoxide radical increased withincreases in oxygen tension in the environment. Moreover, thedevelopment of this system consisted of two steps, namely, arapid increase in the level of glutathione and a subsequentslow increase in the activities of antioxidative enzymes. ¹ Present address: Research Institute for Bioresources, OkayamaUniversity, Kurashiki, 710 Japan.     

Distribution of rhodanese in plants

To study the distribution of rhodanese (E.C. 2.8.1.1) in plants, rhodanese activity was assayed on 13 cyanogenic and 12 non-cyanogenic species. All the species tested had the enzyme activity. This phenomenon leads to a hypothesis that the enzyme is generally distributed in plants.     

Concentration-dependent inducing activity of activin A

Summary Human recombinant activin A, which is identical with erythroid differentiation factor (EDF), was tested for its mesoderm-inducing activity in concentrations from 0.3–50 ng/ml, using ectoderm of Xenopus late blastula (Stage 9) as the responding tissue. At a low concentration of activin A, blood-like cells, mesenchyme, and coelomic epithelium were induced; at a moderate concentration muscle and neural tissue, and at a high concentration notochord. Activin A thus induced all mesodermal tissues in a dose-dependent manner, such that a low dose induced ventral structures and a high dose induced dorsal structures. Activin may act as an intrinsic inducing molecule responsible for establishing the dorso-ventral axis in early Xenopus development. Offprint requests to: M. Asashima