Observations of rotation within the FoF1-ATP synthase: deciding between rotation of the Foc subunit ring and artifact

F(o)F(1)-ATP synthase mediates coupling of proton flow in F(o) and ATP synthesis/hydrolysis in F(1) through rotation of central rotor subunits. A ring structure of F(o)c subunits is widely believed to be a part of the rotor. Using an attached actin filament as a probe, we have observed the rotation of the F(o)c subunit ring in detergent-solubilized F(o)F(1)-ATP synthase purified from Escherichia coli. Similar studies have been performed and reported recently [Sambongi et al. (1999) Science 286, 1722-1724]. However, in our hands this rotation has been observed only for the preparations which show poor sensitivity to dicyclohexylcarbodiimde, an F(o) inhibitor. We have found that detergents which adequately disperse the enzyme for the rotation assay also tend to transform F(o)F(1)-ATP synthase into an F(o) inhibitor-insensitive state in which F(1) can hydrolyze ATP regardless of the state of the F(o). Our results raise the important issue of whether rotation of the F(o)c ring in isolated F(o)F(1)-ATP synthase can be demonstrated unequivocally with the approach adopted here and also used by Sambongi et al.     

A leucine zipper-based peptide hybrid delivers functional Nanog protein inside the cell nucleus

We synthesized a pair of compounds containing leucine zipper peptides to deliver protein cargo into cells. One is a cell-penetrating peptide (CPP) with Lz(E), a leucine zipper peptide containing negatively charged amino acids, and the other is a Nanog protein with Lz(K), a leucine zipper peptide containing positively charged amino acids. When cells were treated with these equimolar mixtures, Nanog-Lz(K) hybridized with Lz(E)-CPP was successfully delivered into the cells. Furthermore, Nanog-Lz(K) exerted its proper function after nuclear transport.     

Telomeric 3' overhangs derive from resection by Exo1 and Apollo and fill-in by POT1b-associated CST

A 3' overhang is critical for the protection and maintenance of mammalian telomeres, but its synthesis must be regulated to avoid excessive resection of the 5' end, which could cause telomere shortening. How this balance is achieved in mammals has not been resolved. Here, we determine the mechanism for 3' overhang synthesis in mouse cells by evaluating changes in telomeric overhangs throughout the cell cycle and at leading- and lagging-end telomeres. Apollo, a nuclease bound to the shelterin subunit TRF2, initiates formation of the 3' overhang at leading-, but not lagging-end telomeres. Hyperresection by Apollo is blocked at both ends by the shelterin protein POT1b. Exo1 extensively resects both telomere ends, generating transient long 3' overhangs in S/G2. CST/AAF, a DNA polα.primase accessory factor, binds POT1b and shortens the extended overhangs produced by Exo1, likely through fill-in synthesis. 3' overhang formation is thus a multistep, shelterin-controlled process, ensuring functional telomeric overhangs at chromosome ends.     

Microbial toxins in plant-pathogen interactions: Biosynthesis,resistance mechanisms,and significance

In the history of phytopathology, microbial toxins have been the objects of extensive studies as possible pathogenicity or virulence factors for the producer pathogens. The recent development of molecular genetic techniques provided an experimental basis to thoroughly test the role of these secondary metabolites in pathogenesis. Some of them did prove to be highly associated with disease initiation or enhanced virulence in certain plant-pathogen interactions. In this review, we describe recent progresses in the field of plant-pathogen interactions focusing on two toxins; i.e., tabtoxin from Pseudomonas syringae and trichothecenes from Fusarium and other fungi. These microbial toxins have convincingly been shown to play causal roles in plant disease development. Studies on the biosynthesis and resistance mechanisms of these producers are outlined, and the significance of this knowledge is discussed in relation to practical applications in agriculture.     

Evaluation of chromosomal risk following intracytoplasmic sperm injection in the mouse

To investigate whether cytogenetic risks occur using the mouse intracytoplasmic sperm injection (ICSI) technique, the incidence of chromosome aberrations was compared in one-cell embryos produced by ICSI technique and those by conventional in vitro fertilization (IVF) technique. Spermatozoa were incubated in TYH medium for 1.5-2 h before IVF insemination. For the ICSI technique, spermatozoa were incubated in five different media: TYH, Hepes-buffered TYH (H-TYH), modified CZB (mCZB), Hepes-buffered mCZB (H-mCZB), and PB1 for 0.5 h, 2-2.5 h, and 6 h before injection into metaphase II oocytes. The incidence of IVF embryos with structural chromosome aberrations was 2%, whereas the occurrence of structural chromosome aberrations in ICSI embryos was dependent on the kind of medium and sperm incubation time. When spermatozoa were incubated in TYH medium for 2 h or more, the aberration rates in the resultant ICSI embryos (4%) were not significantly different from that of IVF embryos. However, there was a significant increase in aberration rates in ICSI embryos derived from spermatozoa that were incubated in other culture conditions (6%-28%). In addition, a time-dependent increase in aberration rates was found in ICSI embryos when H-TYH, H-mCZB, and PB1 were used for sperm incubation. There was no significant difference in incidence of aneuploidy between IVF and ICSI embryos. The chromosome analysis results of one-cell embryos were reflected by the performance of postimplantation embryo development. The causal mechanism of chromosome damage in ICSI embryos was discussed in relation to the plasma membrane cholesterol, the acrosome, and in vitro aging of spermatozoa.     

Plectranthias maekawa,a new species of perchlet from the Tokara Islands,Kagoshima, Japan,with a review of Japanese records of P. wheeleri (Serranidae: Anthiadinae)

Ichthyological Research - A new species of perchlet, Plectranthias maekawa, is described on the basis of three specimens (58.2–65.1 mm standard length: SL) from the Tokara Islands,...