Bacterial group II introns encode maturase proteins required for splicing. In organelles of photosynthetic land plants, most of the group II introns have lost the reading frames for maturases. Here, we show that the plastidial maturase MatK not only interacts with its encoding intron within trnK-UUU, but also with six additional group II introns, all belonging to intron subclass IIA. Mapping analyses of RNA binding sites revealed MatK to recognize multiple regions within the trnK intron. Organellar group II introns are considered to be the ancestors of nuclear spliceosomal introns. That MatK associates with multiple intron ligands makes it an attractive model for an early trans-acting nuclear splicing activity.roup II introns are highly structured ribozymes, found in bacteria and organellar genomes of plants, fungi, protists, and some animals. They catalyze their own excision from precursor RNAs (1). In addition, bacterial group II introns are mobile genetic elements. These features, as well as structural similarities with nuclear introns, have led to the proposition that ancestors of modern group II introns have crossed kingdoms from prokaryotes to eukaryotes via eubacterial endosymbionts, and eventually evolved into nuclear introns (2). Whereas nuclear introns are removed by a large ribonucleoprotein complex called the spliceosome, each bacterial intron encodes a distinct maturase protein facilitating its splicing. The evolutionary transition from the highly specific, maturase-driven splicing toward the complex transacting spliceosomal machinery is unclear. Without any "living fossils" with a protospliceosome, a key question is how the emerging intron diversification was accompanied by a splicing machinery with the ability to act on multiple targets. At least initially, the already existing splicing factors encoded by the invading group II introns, i.e., modified maturases, may have fulfilled this task.In present day organelles, maturase genes can be found in fungal and plant mitochondria as well as in plant chloroplasts. Although mitochondria are not directly amenable to transgenic studies, there are a number of plant species, foremost tobacco, for which directed mutagenesis of chloroplast genomes is possible (3). All land plant chloroplasts with the exception of some parasitic species in the genus Cuscuta (4, 5) contain a single maturase gene called matK in the intron of the lysine tRNA-K (UUU) gene. matK is expressed at least in green tissue (6-8). Sequence and structural homologies are found to the RNA binding motif (domain X) and the reverse transcriptase domain typically found in bacterial maturases (9, 10). Both domains are involved in splicing. By contrast, domains required for the mobility of group II introns are missing in MatK.The function of matK in chloroplasts is so far unknown, but its position inside the trnK gene suggests a role for splicing the trnK precursor. Importantly, it has been suggested that other chloroplast introns are targeted by MatK as well: firstly, several chloroplast genomes o...

The thermal behavior and molecular interaction of a new type of bacterial copolyester, poly-(3-hydroxybutyrate-co-3-hydroxyhexanoate), P(HB-co-HHx) (HHx ) 12 mol %), was investigated by using wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). The WAXD measurements were carried out over a temperature range from 25 to 110 °C in the scattering angle range of 2θ ) 5-13°. The WAXD pattern at room temperature shows that the P(HB-co-HHx) copolymer has an orthorhombic system (R ) β ) γ ) 90°) with a ) 5.76 Å, b ) 13.20 Å, and c ) 5.96 Å (fiber repeat), which is identical to the crystal system of poly(3-hydroxybutyrate) (PHB) homopolymer. However, temperaturedependent variations in the lattice parameters, a and b, of P(HB-co-HHx) are quite different from those of PHB. Only the a lattice parameter increases with temperature, while the b lattice parameter changes very little in the case of crystalline P(HB-co-HHx). It seems that the intermolecular and intramolecular interactions between the CdO group and the CH 3 group decrease along the a axis of crystalline P(HBco-HHx) with temperature. The (110) peak area of P(HB-co-HHx) starts decreasing from around 50 °C while that of PHB changes little at least until 140 °C, indicating that the crystallinity of PHB remains almost unchanged until 140 °C, but that of P(HB-co-HHx) decreases gradually from fairly low temperature (∼50 °C). The DSC measurement of the chloroform solution cast P(HB-co-HHx) shows a recrystallization peak around 51 °C. The (110) peak area of WAXD pattern of the chloroform solution cast P(HB-co-HHx) shows a maximum value at around 54 °C. The maximum of the (110) peak area demonstrates the recrystallization process of P(HB-co-HHx). The result is in a good agreement with the result of the DSC measurement.

Novel isoxazolopyridone derivatives that are metabotropic glutamate receptor (mGluR) 7 antagonists were discovered and pharmacologically characterized. 5-Methyl-3,6-diphenylisoxazolo [4,5-c]pyridin-4(5H)-one (MDIP) was identified by random screening, and 6-(4-methoxyphenyl)-5-methyl-3-pyridin-4-ylisoxazolo [4,5-c] In CHO cells coexpressing human mGluR7 with G␣ 15 , MDIP and MMPIP also inhibited the L-AP4-induced cAMP response. The maximal degree of inhibition by MMPIP was higher than that by MDIP in a cAMP assay. MMPIP was able to antagonize an allosteric agonist, the N,NЈ-dibenzhydryl-ethane-1,2-diamine dihydrochloride (AMN082)-induced inhibition of cAMP accumulation. In the absence of these agonists, MMPIP caused a further increase in forskolin-stimulated cAMP levels in CHO cells expressing mGluR7, whereas a competitive antagonist, LY341495, did not. This result indicates that MMPIP has an inverse agonistic activity. The intrinsic activity of MMPIP was pertussis toxin-sensitive and mGluR7-dependent. MMPIP at concentrations of at least 1 M had no significant effect on mGluR1, mGluR2, mGluR3, mGluR4, mGluR5, and mGluR8. MMPIP is the first allosteric mGluR7-selective antagonist that could potentially be useful as a pharmacological tool for elucidating the roles of mGluR7 on central nervous system functions.Metabotropic glutamate receptors (mGluRs) belong to a family of G protein-coupled receptors thought to contribute to the modulation of neuronal excitability and neurotransmitter release. Eight mGluR subtypes (mGluR1-mGluR8) have been cloned, and they have been classified into three groups based on sequence homology, pharmacological profile, and signal transduction pathway. mGluR1 and mGluR5 belong to group I mGluRs, and they are coupled to phospholipase C and subsequent intracellular calcium release via G q protein. mGluR2 and mGluR3 belong to group II mGluRs, whereas mGluR4, mGluR6, mGluR7, and mGluR8 belong to group III mGluRs. The subtypes of group II and group III mGluRs are negatively coupled to adenylate cyclase via G i protein (Conn and Pin, 1997 , 5-methyl-3,6-diphenylisoxazolo[4,5-c

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