In prokaryotes and archaea transfer ribonucleic acid (tRNA) stability as well as cellular UV protection relies on the post-transcriptional modification of uracil at position 8 (U8) of tRNAs by the 4-thiouridine synthetase ThiI. Here, we report three crystal structures of ThiI from Thermotoga maritima in complex with a truncated tRNA. The RNA is mainly bound by the N-terminal ferredoxin-like domain (NFLD) and the THUMP domain of one subunit within the ThiI homo-dimer thereby positioning the U8 close to the catalytic center in the pyrophosphatase domain of the other subunit. The recognition of the 3’-CCA end by the THUMP domain yields a molecular ruler defining the specificity for U8 thiolation. This first structure of a THUMP/NFLD-RNA complex might serve as paradigm for the RNA recognition by THUMP domains of other proteins. The ternary ThiI–RNA–ATP complex shows no significant structural changes due to adenosine triphosphate (ATP) binding, but two different states of active site loops are observed independent of the nucleotide loading state. Thereby conformational changes of the active site are coupled with conformational changes of the bound RNA. The ThiI–RNA complex structures indicate that full-length tRNA has to adopt a non-canonical conformation upon binding to ThiI.

Si3N4 wird erhalten durch Reaktion von elementarem Silicum mit Stickstoff oder Ammoniak, bzw. durch thermische Zersetzung von Si(NH)2 bei 1350°C. Es existieren zwei polymorphe Modifikationen, α‐Si3N4 und β‐Si3N4. Reines α‐Si3N4 entsteht nur aus Si(NH)2, alle anderen Präparate sind Mischungen der beiden Modifikationen. β‐Si3N4 ist dem Phenakit isotyp, kristallisiert aber wegen der Gleichwertigkeit der Si‐Atome in der Raumgruppe C 6h2 mit a = 7,59 ± 0,01 Å; c = 2,90 ± 0,01 Å; Z = 2; dR = 3,21. ±Si3N4 kristallisiert hexagonal mit a = 7,76 ± 0,01 Å; c = 5,62 ± 0,01 Å; Z = 4; dR = 3,18; das Gitter ist dem des α‐Si3N4 verwandt, Dielektrizitätskonstante (αSi3N4 + β‐Si3N4) ϵ18° = 9,4. Das Verhalten gegenüber verschiedenen Säuren, Basen, Sauerstoff, Wasserdampf, Chlor und Eisen wird studiert. Ab 700° C zersetzt Eisen Si3N4 nach Si3N4 = 3 Si + 2 N2. Die Menge des zersetzten Si3N4 wird durch den Si‐Gehalt der bei der Reaktion entstandenen Fe—Si‐Legierung begrenzt, der von der Temperatur abhängig ist. Die Versuche zeigen, daß Si3N4 als nichtmetallischer Einschluß im Stahl nicht vorkommen kann.

Aus SiCl4 und flüssigem NH3 dargestelltes Si(NH)2 wird bei pNH3 = 50 Torr abgebaut. Folgende Abbaureihe wurde sichergestellt: Außer dem hexagonal kristallisierenden α‐Si3N42 sind alle Verbindungen röntgenamorph und sehr feuchtigkeitsempfindlich. Wahrscheinlich liegen Hochpolymere vor, mit einem nichtperiodischen und nichtsymmetrischen Netzwerk von Si(NH)4‐ bzw. SiN4‐Tetraedern.

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The sulfurtransferase 4-thiouridine synthetase (ThiI) is involved in the ATPdependent modification of U8 in tRNA. ThiI from Thermotoga maritima was cloned, overexpressed and purified. A complex comprising ThiI and a truncated tRNA was prepared and crystallized, and X-ray diffraction data were collected to a resolution of 3.5 Å . The crystals belonged to the orthorhombic space group P2 1 2 1 2 1 , with unit-cell parameters a = 102.9, b = 112.8, c = 132.8 Å .

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The successful treatment of acute and chronic osteomyelitis with the antibiotic lincomycin (Upjohn) has been the subject of several recent reports (Holloway, Kahlbaugh & Scott, 1963;Geddes, Sleet & McMurdoch, 1964;McLeod, Ross, Ozere, Digout & Van Rooyen, 1964;Grondin, St. Martin & Potvin, 1965; Holloway & Scott, 1965;Kaplan, Chew & Weinstein, 1965;McMillan, McRae & McDougall, 1967). While the investigations of Myer & Lewis (1963) and Ma, Lim & Nodine (1963) have elucidated the general pharmacokinetics of lincomycin, knowledge about the concentration in bone is incomplete and more information would be of interest.In osteomyelitis patients treated with lincomycin, Holloway, Kahlbaugh & Scott (1963) found concentrations ranging from 1.1 to 6.6 ug/g of bone. Simultaneous determinations of serum concentrations showed these to be higher than those in bone. As calculated from the data of the authors, the amount found in bone was 13.3 to 18.3% of that in serum.Conflicting results were published by Grady & Stern (1965). In their study in rats, the bone concentration regularly exceeded the serum concentration after a single oral administration of 100 mg/kg of an aqueous lincomycin solution. However, no appreciable binding of lincomycin to bone (for example by chelate formation as with tetracycline) was noted.The experiments described below were carried out to investigate further the concentrations of lincomycin in serum and bone in rats. METHODSNormal albino rats with an average weight of 150 g were used. Each was given a single dose of 20 mg/kg lincomycin HCL. To avoid the wide variation of serum concentration commonly observed after oral administration because of variability in absorption, the dose was injected intramuscularly in aqueous solution. Animals were killed at intervals after the dose and the lincomycin content of serum and bone assayed. In the second part of the study 10 rats were treated with repeated injections of 20 mg/kg 12-hourly for 6 days and on the morning of the seventh day. Antibiotic concentrations in bone and serum of 2 animals were determined 1, 1, 2, 4 and 6 hr after the last injection. For all experiments lincomycin hydrochloride was used, provided in vials containing 20 mg. (Upjohn, Lot 14,.The concentration of the antibiotic in serum and bone was determined by means of the agar diffusion technique (cup plate method). The agar was autoclaved and then adjusted to pH 7.8.