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The soil bacterium Arthrobacter nitroguajacolicus Ru61a contains the linear plasmid pAL1, which codes for the degradation of 2-methylquinoline. Like other linear replicons of actinomycetes, pAL1 is characterized by short terminal inverted-repeat sequences and terminal proteins (TPpAL1) covalently attached to its 5' ends. TPpAL1, encoded by the pAL1.102 gene, interacts in vivo with the protein encoded by pAL1.101. Bioinformatic analysis of the pALl.101 protein, which comprises 1,707 amino acids, suggested putative zinc finger and topoisomerase-primase domains and part of a superfamily 2 helicase domain in its N-terminal and central regions, respectively. Sequence motifs characteristic of the polymerization domain of family B DNA polymerases are partially conserved in a C-terminal segment. The purified recombinant protein catalyzed the deoxycytidylation of TPpAL1 in the presence of single-stranded DNA templates comprising the 3'-terminal sequence (5'-GCAGG-3'), which in pAL1 forms the terminal inverted repeat, but also at templates with 5'-(G/T)CA(GG/GC/CG)-3' ends. Enzyme assays suggested that the protein exhibits DNA topoisomerase, DNA helicase, and DNA- and protein-primed DNA polymerase activities. The pALl.101 protein, therefore, may act as a replicase of pAL1. doi: 10.1128/JB.00614-10

Light is necessary for photosynthesis, but its absorption by pigment molecules such as chlorophyll can cause severe oxidative damage and result in cell death. The excess absorption of light energy [...]

The molecular coordination compound trans-[Cu[Cl.sub.2][(3-Clpy).sub.2]] (3-Clpy = 3-chloropyridine), which is prepared as a microcrystalline powder, is reacted directly with gaseous HCl in the absence of water to yield the crystalline salt [(3-ClpyH).sub.2][Cu[Cl.sub.4]]. The reversible uptake of HCl molecules from the gas phase by a nonporous crystalline solid has proceeded in the absence of any solvent and with retention of crystallinity, despite many changes that are required by this process.

We used fast absorbance spectroscopy to investigate in vivo binding dynamics and electron transfer between plastocyanin (pc) and photosystem I (PSI), and cytochrome (cyt) f oxidation kinetics in Chlamydomonas reinhardtii mutants in which either the binding or the release of pc from PSI was diminished. Under single flash-excitation conditions, electron flow between PSI and the cyt complex was not affected by a 5-fold lowering of the binding affinity of pc to PSI, as induced by a mutation replacing the tryptophan-651 of the PsaA subunit by a serine residue (PsaA-W651S). On the other hand, electron flow from PSI to the cyt [b.sub.6]f complex was very sensitive to a 2- to 3-fold decrease in the rate of pc release from PSI, obtained by replacing the glutamic acid residue 613 of the PsaB subunit with glutamine (PsaB-E613N). Thus, our data indicate that under these experimental conditions the release of oxidized pc limits electron transfer between cyt [b.sub.6]f complex and PSI in vivo. Chlamydomonas | photosynthesis | protein-protein interactions | systems biology

Plants protect themselves against herbivory with a diverse array of repellent or toxic secondary metabolites. However, many herbivorous insects have developed counteradaptations that enable them to feed on chemically defended plants without apparent negative effects. Here, we present evidence that larvae of the specialist insect, Pieris rapae (cabbage white butterfly, Lepidoptera: Pieridae), are biochemically adapted to the glucosinolatemyrosinase system, the major chemical defense of their host plants. The defensive function of the glucosinolate--myrosinase system results from the toxic isothiocyanates that are released when glucosinolates are hydrolyzed by myrosinases on tissue disruption. We show that the hydrolysis reaction is redirected toward the formation of nitriles instead of isothiocyanates if plant material is ingested by P. rapae larvae, and that the nitriles are excreted with the feces. The ability to form nitriles is due to a larval gut protein, designated nitrile-specifier protein, that by itself has no hydrolytic activity on glucosinolates and that is unrelated to any functionally characterized protein. Nitrile-specifier protein appears to be the key biochemical counteradaptation that allows P. rapae to feed with impunity on plants containing glucosinolates and myrosinases. This finding sheds light on the ecology and evolution of plant--insect interactions and suggests novel highly selective pest management strategies.

The functionality of PsaF with respect to the photosystem I complex is diminished due to a displacement of the N-terminal domain of the subunit. This is evident in an experiment in which the psaJ chloroplast gene of the green alga Chlamydomonas reinhardtii was inactivated either in a wild-type or in a PsaF-deficient nuclear background. The N-terminal domain of PsaF is exposed in the lumenal space in the absence of PsaJ when the domain is cross-linked to Pc and Cyt c(sub 6). It is suggested that PsaJ maintains PsaF in a proper orientation and results in fast electron transfer from soluble donor proteins to P700(super +).

The PsaF-deficient mutant 3bF of Chlamydomonas reinhardtii was used to modify PsaF by nuclear transformation and site-directed mutagenesis. Four lysine residues in the N-terminal domain of PsaF, which have been postulated to form the positively charged face of a putative amphipathic [Alpha]-helical structure were altered to K12P, K16Q, K23Q, and K30Q. The interactions between plastocyanin (pc) or cytochrome [c.sub.6] (cyt [c.sub.6]) and photosystem I (PSI) isolated from wild type and the different mutants were analyzed using crosslinking techniques and flash absorption spectroscopy. The K23Q change drastically affected crosslinking of pc to PSI and electron transfer from pc and cyt [c.sub.6] to PSI. The corresponding second order rate constants for binding of pc and cyt [c.sub.6] were reduced by a factor of 13 and 7, respectively. Smaller effects were observed for mutations K16Q and K30Q, whereas in K12P the binding was not changed relative to wild type. None of the mutations affected the half-life of the microsecond electron transfer performed within the intermolecular complex between the donors and PSI. The fact that these single amino acid changes within the N-terminal domain of PsaF have different effects on the electron transfer rate constants and dissociation constants for both electron donors suggests the existence of a rather precise recognition site for pc and cyt [c.sub.6] that leads to the stabilization of the final electron transfer complex through electrostatic interactions.

Cross-linking techniques and flash absorption spectroscopy were used to determine the interactions between plastocyanin or cytochrome c6 with photosystem I (PSI) from wild-type and a PsaF-deficient mutant of Chlamydomonas reinhardtii. Results reveal that efficient electron transfer from cytochrome c6 and plastocyanin to photosystem I of C. reinhardtii requires PsaF. It is also found that the PSI complex of C. reinhardtii is remarkably different from other photosynthetic organisms since its plastocyanin and cytochrome c6 reduce P700+ with first order kinetics and a half-time of 3 mus.

The process of electron transfer from the soluble protein plastocyanin to the multiprotein complex of photosystem I from spinach was examined. The individual dissociation constants of the complex between the proteins in all oxidized and reduced states was determined by monitoring the effect of increasing the amount of reduced plastocyanin on the kinetic components and the competition by oxidized plastocyanin. Findings indicated that a substantial portion of the energy for electron transfer is diverted to photosystem I.

The design and performance of an affordable Raman spectrometer are described. The equipment is based on a compact monochromator and on a 4mW 532 nm green laser pointer. The spectrometer can be used for applicable for fundamental research, analytical applications, and different graduate and undergraduate research.

The N = 2 triad involving excitations with two quanta of hydrogen fluoride (HF) stretching in HF dimer [(HF).sub.2] around 1.3 [mu]m are studied by using continuous-wave-diode laser cavity ring-down spectrsocopy in a pulsed supersonic slit jet expansion. The studies have shown that the N = 2 triad has displayed a strongly mode-selective predissociation dynamics.

The composition of light harvesting complex I (LHCI) of a tomato is examined. The findings indicate that several populations of the photosystem I that differ in their Lhca composition may exist.

The subunit compositions of the PSI-LHCI (photosystem I -light-harvesting chlorophyll protein complex I)supercomplex and the LHCI by immunoblot analysis and two-dimensional gel electrophoresis combined with mass spectrometry is examined. The possible localization and function of Lhca polypeptides in the LHCI is discussed.

The isotopmer selected N = 2 CH chromophore absorption of (super 12)C(sub 6)H(sub 6) and (super 13)C(super 12)C(sub 5)H(sub 6) near 6000 cm(super -1) at natural abundance are recorded. The (super 12)C(sub 6)H(sub 6) spectrum is compatible with a proposed model of intramolecular vibrational redistribution with a distinct hierarchy of time scales.

Several elementary steps, which are defined in molecularity and reaction order, in a photochemical reaction system, are discussed. In this, the elementary or primary absorption step is considered as bimolecular reaction.