Synthesis of the Rhodopseudomonas viridis holo-cytochrome c2 in Paracoccus denitrificans

Abstract The gene encoding the Rhodopseudomonas viridis cytochrome c ₂ (cycA) has been introduced on a broad host range vector into Paracoccus denitrificans , leading to high-level expression of the holo-cytochrome with the heme moiety covalently attached to the apoprotein. The cytochrome was demonstrated to reside in the periplasmic space of the host cell. In contrast to R. viridis , aerobic rather than anaerobic growth conditions led to higher production levels of the holo-cytochrome in P. denitrificans . This heterologous expression system provides a suitable genetic background for the functional expression and mutagenesis of polypeptides involved in bacterial photosynthesis, offering the possibility of detailed structural and functional investigation.     

CFM1, a member of the CRM-domain protein family,functions in chloroplast group II intron splicing in Setaria viridis

The chloroplast RNA splicing and ribosome maturation (CRM) domain is a RNA-binding domain found in a plant-specific protein family whose characterized members play essential roles in splicing group I and group II introns in mitochondria and chloroplasts. Together, these proteins are required for splicing of the majority of the approximately 20 chloroplast introns in land plants. Here, we provide evidence from Setaria viridis and maize that an uncharacterized member of this family, CRM Family Member1 (CFM1), promotes the splicing of most of the introns that had not previously been shown to require a CRM domain protein. A Setaria mutant expressing mutated CFM1 was strongly disrupted in the splicing of three chloroplast tRNAs: trnI, trnV and trnA. Analyses by RNA gel blot and polysome association suggest that the tRNA deficiencies lead to compromised chloroplast protein synthesis and the observed whole-plant chlorotic phenotypes. Co-immunoprecipitation data demonstrate that the maize CFM1 ortholog is bound to introns whose splicing is disrupted in the cfm1 mutant. With these results, CRM domain proteins have been shown to promote the splicing of all but two of the introns found in angiosperm chloroplast genomes.     

High-resolution optical absorption-difference spectra of the triplet state of the primary donor in isolated reaction centers of the photosynthetic bacteria Rhodopseudomonas sphaeroides R-26 and Rhodopseudomonas viridis measured with optically detected magnetic resonance at 1.2 K

We have recorded triplet optical absorption-difference spectra of the reaction center triplet state of isolated reaction centers from Rhodopseudomonas sphaeroides R-26 and Rps. viridis with optical absorption-detected electron spin resonance in zero magnetic field (ADMR) at 1.2 K. This technique is one to two orders of magnitude more sensitive than conventional flash absorption spectroscopy, and consequently allows a much higher spectral resolution. Besides the relatively broad bleachings and appearances found previously (see, e.g., Shuvalov V.A. and Parson W.W. (1981) Biochim. Biophys. Acta 638, 50–59) we have found strong, sharp oscillations in the wavelength regions 790–830 nm (Rps. sphaeroides) and 810–890 nm (Rps. viridis). For Rps. viridis these features are resolved into two band shifts (a blue shift at about 830 nm and a red shift at about 855 nm) and a strong, narrow absorption band at 838 nm. For Rps. sphaeroides R-26 the features are resolved into a red shift at about 810 nm and a strong absorption band at 807 nm. We conclude that the appearance of the absorption bands at 807 and 838 nm, respectively, is due to monomeric bacteriochlorophyll. Apparently, the exciton interaction between the pigments constituting the primary donor is much weaker in the triplet state than in the singlet state, and at low temperature the triplet is localized on one of the bacteriochlorophylls on an optical time scale. The fact that for Rps. sphaeroides the strong band shift and the monomeric band found at 1.2 K are absent at 293 K and very weak at 77 K indicates that these features are strongly temperature dependent. It seems, therefore, premature to ascribe the temperature dependence between 293 and 77 K of the intensity of the triplet absorption-difference spectrum at 810 nm (solely) to a delocalization of the triplet state on one of the accessory bacteriochlorophyll pigments.     

Evidence for two Qa-like quinone binding sites in the reaction centre of Rhodopseudomonas viridis

The oxidation-reduction potential of the iron-quinone electron acceptors in the reaction centre of Rhodopseudomonas viridis has been reinvestigated. In chromatophores treated with o-phenanthroline to remove the secondary acceptor Q_b, two steps were observed in the reduction of the primary electron acceptor Q_a with E_m ≈ − 100 and ≈ − 330 mV. In isolated reaction centres only one step was observed in the reduction of Q_a with E ≈ −150 mV. Reconstitution of the reaction centres with additional menaquinone resulted in an increase in the Q_a EPR signal and reconstitution of the low-potential step in the oxidation-reduction titration. Reconstitution with ubiquinone resulted in the recovery of the secondary quinone Q_b. The addition of ubiquinone did not reconstitute the low-potential step of Q_a reduction, or affect the reconstitution of this step by menaquinone. It is concluded that menaquinone can bind to two sites on the reaction centre. Both have properties of the Q_a site but with different pK values. It is unlikely that either is the same as the Q_b site.     

Efficient photochemical activity and strong dichroism of single crystals of reaction centers from Rhodopseudomonas viridis

Crystallized reaction centers from Rhodopseudomonas viridis (i) are photochemically active with electron transfer from the special pair to the quinones, (ii) show dichroism giving valuable information on the orientation of the different chromophores and (iii) allow chemical treatment in the crystalline phase.     

Effects of Bonellin on fertilization and cleavage of the eggs of the sea urchin,sphaerechinus granularis

We have studied the structural changes occurring in the eggs of the sea urchin Sphaerechinus granularis treated with bonellin, the green pigment of the sea worm Bonellia viridis, which is responsible for the masculinization of the larva of this animal. The two major targets of bonellin appear to be the cortical structures and the nuclear membrane, while the mitochondria do not appear to be affected. As a result of bonellin treatment, cleavage is prevented while nuclear divisions proceed. The possibility is discussed that the alteration of the cortical structures may interfere with the assembly of the surface microfilaments and hence with the formation of the cleavage furrows.     

Chemical cues from predators and damaged conspecifics affect byssus production in the green-lipped mussel perna viridis

Juveniles of the green-lipped mussel Perna viridis (Bivalvia: Mytilidae) were exposed to either chemical cues of damaged conspecifics or predator, including the swimming crab Thalamita danae and the muricid gastropod Thais clavigera. Byssus production was monitored for 48?h but the highest production rate occurred in the first 6?h. Longer and thicker byssal threads with a larger total volume were produced by P. viridis exposed to damaged conspecifics and predators as compared with the control. Numbers of individuals which shed stalks during the experiment varied significantly from 0 to 50%, and with a significantly higher value obtained for the control. Results indicated that byssus production is a plastic response which could be induced by exposure to chemical signals from predators and damaged conspecifics, the latter producing the largest response. Firmer byssal attachment not only reduces predation risk but also non-predation mortality by securing an animal more effectively to its habitat.     

Distribution of clinically important thermophilic actinomycetes in vegetable substrates and soil in north-western India

Medically important thermophilic actinomycetes were isolated from 218 (64%) of 341 samples of vegetable substrates and soil examined from sites in north-western India. Thermoactinomyces vulgaris (T. candidus) was the commonest species, occurring in 56% of samples, followed by Saccharomonospora viridis in 29%, Thermoactinomyces thalpophilus in 27%, Faenia rectivirgula (Micropolyspora faeni) in 21% and Thermoactinomyces sacchari in 14%. T. vulgaris and T. thalpophilus were isolated from all types of substrate examined, with T. vulgaris always more common than T. thalpophilus. Of the other thermophilic actinomycetes, F. rectivirgula was isolated predominantly from hay (44%) and S. viridis (56%) and T. sacchari (44%) from sugarcane bagasse. The largest populations of T. vulgaris and T. thalpophilus were found in paddy straw, followed by T. sacchari, S. viridis and F. rectivirgula in sugar-cane bagasse.The widespread occurrence of these clinically important thermophilic actinomycetes suggests that exposure of humans and animals to them may be frequent in north-western India. Studies are required to determine the prevalence of extrinsic allergic alveolitis (hypersensitivity pneumonitis) caused by thermophilic actinomycetes in the local population.