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281.
Common thiolation mechanism in the biosynthesis of tRNA thiouridine and sulphur‐containing cofactors
Naoki Shigi Yuriko Sakaguchi Shin‐ichi Asai Tsutomu Suzuki Kimitsuna Watanabe 《The EMBO journal》2008,27(24):3267-3278
2‐Thioribothymidine (s2T), a modified uridine, is found at position 54 in transfer RNAs (tRNAs) from several thermophiles; s2T stabilizes the L‐shaped structure of tRNA and is essential for growth at higher temperatures. Here, we identified an ATPase (tRNA‐two‐thiouridine C, TtuC) required for the 2‐thiolation of s2T in Thermus thermophilus and examined in vitro s2T formation by TtuC and previously identified s2T‐biosynthetic proteins (TtuA, TtuB, and cysteine desulphurases). The C‐terminal glycine of TtuB is first activated as an acyl‐adenylate by TtuC and then thiocarboxylated by cysteine desulphurases. The sulphur atom of thiocarboxylated TtuB is transferred to tRNA by TtuA. In a ttuC mutant of T. thermophilus, not only s2T, but also molybdenum cofactor and thiamin were not synthesized, suggesting that TtuC is shared among these biosynthetic pathways. Furthermore, we found that a TtuB—TtuC thioester was formed in vitro, which was similar to the ubiquitin‐E1 thioester, a key intermediate in the ubiquitin system. The results are discussed in relation to the mechanism and evolution of the eukaryotic ubiquitin system. 相似文献
282.
The formation of the micropylar apparatus during oogenesis in the silkworm, Bombyx mori, has been studied using light and transmission electron microscopy. The micropylar apparatus is formed by three types of cells: the micropylar channel-forming cells (MCFCs), the micropylar orifice-forming cells (MOFCs), and the micropylar rosette-forming cells (MRFCs). During the formation of the vitelline membrane and the chorion, each of the MCFCs extends a cytoplasmic projection serving as the mold of a micropylar-channel into the egg envelopes. The detachment and collapse of the projections takes place at the end of choriogenesis. The micropylar channels possess a common external orifice on the chorion and several internal orifices within the vitelline membrane. The MOFCs interact closely with the MCFCs and contribute to the formation of the external micropylar orifice. A petal-like rosette surrounding the orifice is imprinted on the outer chorionic surface by the MRFCs which enclose a group of the MCFCs and MOFCs. 相似文献
283.
Oogenesis in the silkworm, Bombyx mori, was studied by light and electron microscopy of sections of resin-embedded follicles. The development of the follicles was divided into a series of 12 distinctive stages based on various morphological criteria. Structural changes in the oocyte, nurse cells, and follicle cells are described and illustrated. 相似文献
284.
Sclerotinia trillii n. sp., which attacksTrillium tschonoskii andT. smallii in Hokkaido and northern Honshu, Japan, is described. The characters identifying this species with the genusSclerotinia are large tuberoid sclerotia, produced both on infected plants and in culture, which consisted of only mycelium (true sclerotia)
and flesh apothecia produced on them. This species is distinguished fromS. sclerotiorum, S. minor, S. trifoliorum, andS. nivalis by relatively large sclerotia, cultural colony appearance, and red-brown to yellow-brown, relatively large apothecium, in
addition to its parasitic nature onTrillium. Sclerotinia trillii is a psychrophilic having an optimum temperature for mycelial growth at 15–20°C. 相似文献
285.
Addition of norepinephrine or isoproterenol to primary cultures started from the brains of 1-3 day old rats caused up to 200-fold increases in cAMP levels, which reached a maximum by 5-10 min and then declined. This effect was studied in detail for norepinephrine. The rise in cAMP levels was followed by morphological changes, in which up to 65% of the cells exhibited an astrocyte-like morphology, and 2-3 fold increases in carbonic anhydrase and (Na+-K+) ATPase activities. However, morphological transformation also occurred after much smaller increases in total cAMP levels. These effects on cell morphology and enzyme activities reached a maximum 1-2 h after addition of norepinephrine and then declined. Carbonic anhydrase activity was found both in the particulate and post 100,000 g supernatant fractions from homogenates of these cultured cells, and in the latter case the activity was activated 3-fold by addition of cAMP. The significance of these obscrvations on the cellular localization of, and functional role for similar increases in cAMP in brain tissue is discussed. 相似文献