Open Access

Background Today it is widely accepted that plastids are of cyanobacterial origin. During their evolutionary integration into the metabolic and regulatory networks of the host cell the engulfed cyanobacteria lost their independency. This process was paralleled by a massive gene transfer from symbiont to the host nucleus challenging the development of a retrograde protein translocation system to ensure plastid functionality. Such a system includes specific targeting signals of the proteins needed for the function of the plastid and membrane-bound machineries performing the transfer of these proteins across the envelope membranes. At present, most informations on protein translocation are obtained by the analysis of land plants. However, the analysis of protein import into the primitive plastids of glaucocystophyte algae, revealed distinct features placing this system as a tool to understand the evolutionary development of translocation systems. Here, bacterial outer membrane proteins of the Omp85 family have recently been discussed as evolutionary seeds for the development of translocation systems. Results To further explore the initial mode of protein translocation, the observed phenylalanine dependence for protein translocation into glaucophyte plastids was pursued in detail. We document that indeed the phenylalanine has an impact on both, lipid binding and binding to proteoliposomes hosting an Omp85 homologue. Comparison to established import experiments, however, unveiled a major importance of the phenylalanine for recognition by Omp85. This finding is placed into the context of the evolutionary development of the plastid translocon. Conclusion The phenylalanine in the N-terminal domain signs as a prerequisite for protein translocation across the outer membrane assisted by a primitive translocon. This amino acid appears to be optimized for specifically targeting the Omp85 protein without enforcing aggregation on the membrane surface. The phenylalanine has subsequently been lost in the transit sequence, but can be found at the C-terminal position of the translocating pore. Thereby, the current hypothesis of Omp85 being the prokaryotic contribution to the ancestral Toc translocon can be supported.

Wer hat nicht angesichts rauchender Schlote und verschmutzter Luft von Kraftwerken geträumt, die reinen Sauerstoff produzieren? Die Natur erbaut solche Kraftwerke täglich neu – in Pflanzen. Darin verwandelt der grüne Blattfarbstoff Chlorophyll Sonnenlicht und Kohlendioxid in Sauerstoff und Energie. Die komplexen Reaktionen laufen in mikroskopisch kleinen Maschinen – den Photosystemen – ab. Aber was haben Kraftwerke mit Kamelen zu tun? Wie auch bei den uns bekannten Kraftwerken gibt es in Pflanzen ein »Werksgelände«, die Chloroplasten. Sie besitzen einen Eingang, durch den zuweilen Moleküle passieren müssen, die so groß sind wie das sprichwörtliche Kamel, das durch ein Nadelöhr gehen soll.

Eukaryotic ribosome biogenesis requires the concerted action of numerous ribosome assembly factors, for most of which structural and functional information is currently lacking. Nob1, which can be identified in eukaryotes and archaea, is required for the final maturation of the small subunit ribosomal RNA in yeast by catalyzing cleavage at site D after export of the preribosomal subunit into the cytoplasm. Here, we show that this also holds true for Nob1 from the archaeon Pyrococcus horikoshii, which efficiently cleaves RNA-substrates containing the D-site of the preribosomal RNA in a manganese-dependent manner. The structure of PhNob1 solved by nuclear magnetic resonance spectroscopy revealed a PIN domain common with many nucleases and a zinc ribbon domain, which are structurally connected by a flexible linker. We show that amino acid residues required for substrate binding reside in the PIN domain whereas the zinc ribbon domain alone is sufficient to bind helix 40 of the small subunit rRNA. This suggests that the zinc ribbon domain acts as an anchor point for the protein on the nascent subunit positioning it in the proximity of the cleavage site.

TAp63a, a homolog of the p53 tumor suppressor, is a quality control factor in the female germline. Remarkably, already undamaged oocytes express high levels of the protein, suggesting that TAp63a’s activity is under tight control of an inhibitory mechanism. Biochemical studies have proposed that inhibition requires the C-terminal transactivation inhibitory domain. However, the structural mechanism of TAp63a inhibition remains unknown. Here, we show that TAp63a is kept in an inactive dimeric state. We reveal that relief of inhibition leads to tetramer formation with ~20-fold higher DNA affinity. In vivo, phosphorylation-triggered tetramerization of TAp63a is not reversible by dephosphorylation. Furthermore, we show that a helix in the oligomerization domain of p63 is crucial for tetramer stabilization and competes with the transactivation domain for the same binding site. Our results demonstrate how TAp63a is inhibited by complex domain-domain interactions that provide the basis for regulating quality control in oocytes.

Heat stress transcription factors (HSFs) regulate transcriptional response to a large number of environmental influences, such as temperature fluctuations and chemical compound applications. Plant HSFs represent a large and diverse gene family. The HSF members vary substantially both in gene expression patterns and molecular functions. HEATSTER is a web resource for mining, annotating, and analyzing members of the different classes of HSFs in plants. A web-interface allows the identification and class assignment of HSFs, intuitive searches in the database and visualization of conserved motifs, and domains to classify novel HSFs.