Cytologische Grundlagen für Sterilitätserscheinungen in der GattungSalvia

Zusammenfassung Die GattungSalvia weist verschiedenartige Sterilitätserscheinungen auf. Die Gynodiözie vonSalvia nemorosa kommt dadurch zustande, daß im Stadium des Diplotän der Meiosis die Pollenmutterzellen degenerieren.BeiS. officinalis erzeugten amitotische Teilungen der Interphasekerne hypohaploide Zellen in Mehrkerntetraden. Da alle, auch der kleinste Mikronukleus, stets einen Nukleolus enthalten, wurde die Frage diskutiert, ob Störungen im Nukleinsäure-Haushalt die Ursache dafür sein könnten. Viele Arten vonSalvia zeigen Cytomixis, vermutlich eine praemortale Reizreaktion der Pollenmutterzellen, die ebenfalls die Ursache für Pollensterilität sein könnte.Mit 5 TextabbildungenHerrn Prof.H. Kappert zum 65. Geburtstag gewidmet     

Redundant mitochondrial targeting signals in yeast adenylate kinase

Yeast adenylate kinase (Aky2p, Adk1p) occurs simultaneously in cytoplasm and mitochondrial intermembrane space. It has no cleavable mitochondrial targeting sequence, and the signal for mitochondrial import and submitochondrial sorting is largely unknown. The extreme N terminus of Aky2p is able to direct cytoplasmic passengers to mitochondria. However, an Aky2 mutant lacking this sequence is imported with about the same efficiency as the wild type. To identify possible import-relevant information in the interior, parts of Aky2p were exchanged by homologous in vitro recombination for the respective segments of the purely cytoplasmic isozyme, Ura6p. Import studies revealed an internal region of about 40 amino acids, which was sufficient to direct the chimera to mitochondria but not for correct submitochondrial sorting. The respective Ura6p hybrid was arrested in the mitochondrial membrane at a position where it was inaccessible to protease but was released by alkaline extraction, suggesting that it had entered an import channel and passed the initial steps of recognition and uptake. Site-specific mutations within the presumptive address-specifying segment identified the amphipathic helix 5. A Ura6 mutant protein in which helix 5 had been replaced with the respective sequence from Aky2p was imported, and this address sequence cooperates with the N terminus in the respective double mutant in a synergistic fashion.     

Activation mechanism of pro-astacin: role of the pro-peptide,tryptic and autoproteolytic cleavage and importance of precise amino-terminal processing

Astacin (EC 3.4.24.21) is a prototype for the astacin family and for the metzincin superfamily of zinc peptidases, which comprise membrane-bound and secreted enzymes involved in extracellular proteolysis during tissue development and remodelling. Generally, metzincins are translated as pro-enzymes (zymogens), which are activated by removal of an N-terminal pro-peptide. In astacin, however, the mode of zymogen activation has been obscured, since the pro-form does not accumulate in vivo. Here we report the detection of pro-astacin in midgut glands of brefeldin A-treated crayfish (Astacus astacus) by immunoprecipitation and mass spectrometry. We demonstrate that the pro-peptide is able to shield the active site of mature astacin as a transient inhibitor, which is degraded slowly. In vitro studies with recombinant pro-astacin in the absence of another protease reveal a potential of auto-proteolytic activation. The initial cleavage in this autoactivation appears to be an intramolecular event. This is supported by the fact that the mutant E93A-pro-astacin is incapable of autoactivation, and completely resistant to cleavage by mature astacin. However, this mutant is cleaved by Astacus trypsin within the pro-peptide. This probably reflects the in vivo situation, where Astacus trypsin and astacin work together during pro-astacin activation. In a first step, trypsin produces amino-terminally truncated pro-astacin derivatives. These are trimmed subsequently by each other and by astacin to yield the mature amino terminus, which forms a salt-bridge with Glu103 in the active site. The disruption of this salt-bridge in the mutants E103A and E103Q results in extremely heat labile proteins, whose catalytic activities are not altered drastically, however. This supports a concept according to which the linkage of Glu103 to the precisely trimmed amino terminus is a crucial structural prerequisite throughout the astacin family.     

über die umbildung einer „meduse” von Craspedacusta sowerbii lank. in eine frustel

Zusammenfassung In einem fur das Massenauftreten des Süßwasserpolypen Craspedacusta-sowerbii Lank. sehr günstigen Aquarium wurde ein ovales, aus dunklem Ektoderm und hellem Ektoderm bestehendes und mit etwa 14–16 Tentakeln ausgestattetes Gebilde gefunden. Nach 24 Std war daraus ein länglich wurstförmiges, sich wie eine normale Frustel fortbewegendes Stadium mit 8–12 verkleinerten Tentakeln geworden. Nach weiteren 10 Std hörte die Fortbewegung auf, die Frustel war kurz und breit und zeigte auch im Zeitrafferlaufbild nur noch geringfügige Kontraktionen. Nach Besprechung der Möglichkeiten wird als sebr wahrscheinlich angenommen, daß eine bis zum Germanica-Stadium entwickelte Meduse sich (in Parallele zum gleichen Vorgang beim Polypen) zurückbildete und dann sich zur Frustel umbildete. Ob die darauffolgende, nicht gelungene Umbildung zum Polypen auf ungünstige äußere Umstände zurückzuführen oder überhaupt nicht möglich ist, kann an einem einzelnen Exemplar nicht entschieden werden. Es wird die Vermutung ausgesprochen, daß die auf dem 8- and 16-Tentakelstadium sich befindenden abortiven Medusen nicht absterben, sondern sich rückzubilden imstande sind.     

Eine neuere Beobachtung über Antibiose bei Pseudomonas-Bakterien

Zusammenfassung In der Reihe der Leguminosenviren wurden zwei weitere Viren vermessen. Dabei ergab sich für das Weißkleevirus eine Normallänge von 476 m und für das Steinkleevirus eine solche von 616 m. Beide Viren sind damit von den Viren des Gewöhnlichen und des Gelben Bohnenmosaiks (mit je 750 m Länge) deutlich unterscheidbar.     

Use of Tn KPK2 for sequencing a 10.6-kb PstI DNA fragment of Bradyrhizobium japonicum and for the construction of aspA and ndvA mutants

Transposon TnKPK2 was used to saturate a randomly cloned Bradyrhizobium japonicum PstI fragment and the insertions were used as starting points for the sequence determination. The first gene of the 10.6-kb DNA insert encodes a homologue to ndvA, the product of which is known to be involved in the formation of periplasmic cyclic glucans. Selected TnKPK2 insertions were introduced into the B. japonicum wild-type strain. The resulting mutants were subsequently tested for their symbiotic interactions with soybeans. As in Sinorhizobium meliloti, a B. japonicum ndvA mutant was affected in salt-stress tolerance and exhibited symbiotic defects in that it induced the formation of ineffective soybean nodules. The central nodule tissue was infected by bacteroids, but within the infected cells the mutant was not properly maintained. Another gene was found to be highly similar to bacterial aspartases and thus was named aspA. The putative function of the product of this gene was confirmed by genetic complementation of aspartase-less Escherichia coli strain TK237. The symbiotic phenotype of a B. japonicum aspATnKPK2 mutant consisted of enlarged symbiosomes that made the system ineffective. In general, TnKPK2 is a suitable means for fast sequencing. In combination with pJQ200SK, the resulting recombinant plasmids can be directly used to create genetically defined mutants.