["Magic spot" synthase in chloroplasts].
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Chloroplasts↗
Biomedical subjects
Yuzuru Tozawa
Publications and source records attributed to Yuzuru Tozawa.
A RelA-SpoT homolog (Cr-RSH) identified in Chlamydomonas reinhardtii generates stringent factor in vivo and localizes to chloroplasts in vitro.
A gene encoding a putative guanosine 3',5'-bispyrophosphate (ppGpp) synthase-degradase, designated Cr-RSH, was identified in the unicellular photosynthetic eukaryote Chlamydomonas reinhardtii. The encoded Cr-RSH protein possesses a putative chloroplast-targeting signal at its NH2-terminus, and translocation of Cr-RSH into chloroplasts isolated from C.reinhardtii was demonstrated in vitro. The predicted mature region of Cr-RSH exhibits marked similarity to eubacterial members of the RelA-SpoT family of proteins. Expression of an NH2-terminal portion of Cr-RSH containing the putative ppGpp synthase domain in a relA, spoT double mutant of Escherichia coli complemented the growth deficits of the mutant cells. Chromatographic analysis of 32P-labeled cellular mononucleotides also revealed that expression of Cr-RSH in the mutant bacterial cells resulted in the synthesis of ppGpp. SpoT, which catalyzes (p)ppGpp degradation, is dispensable in E.coli only if cells also lack RelA, which possesses (p)ppGpp synthase activity. The complementation analysis thus indicated that Cr-RSH possesses both ppGpp synthase and degradase activities. These results represent the first demonstration of ppGpp synthase-degradase activities in a eukaryotic organism, and they suggest that eubacterial stringent control mediated by ppGpp has been conserved during evolution of the chloroplast from a photosynthetic bacterial symbiont.
Amino Acid Sequence↗
Genetic and physiological characterization of rpoB mutations that activate antibiotic production in Streptomyces lividans.
Antibiotic production in Streptomyces lividans can be activated by introducing certain mutations (rif) into the rpoB gene that confer resistance to rifampicin. Working with the most typical (rif-17) mutant strain, KO-417, the rif-17 mutation was characterized. The rif-17 mutation was shown to be responsible for activating antibiotic production and for reducing the growth rate of strain KO-417, as demonstrated by gene-replacement experiments. Gene-expression analysis revealed that introduction of rif into S. lividans elevates expression of the pathway-specific regulatory gene actII-ORF4 to nearly the same level seen in Streptomyces coelicolor. The rif effect on antibiotic production was still evident in the genetic background of relC, indicating that the rif mutation can provoke its effect without depending on ppGpp. Accompanying the restoration of antibiotic production, rif mutants also exhibited a lower rate of RNA synthesis compared to the parental strain when grown in a nutritionally rich medium, suggesting that the mutant RNA polymerases may behave like 'stringent' RNA polymerases. These results indicate that the rif mutation can alter the gene-expression pattern independent of ppGpp. The impaired growth of strain KO-417 (rif-17) was largely restored by introducing the second rif mutation (rif-18) just adjacent to the rif-17 position. Proteome analysis using two-dimensional PAGE revealed that the rif mutant strain KO-418 (rif-17 rif-18) displayed a temporal burst of expression especially of two enzymes, glutamine synthetase (type II) and oxidoreductase, during the late growth phase.
Amino Acids↗
OsRALyase1, a putative F-box protein identified in rice, Oryza sativa, with enzyme activity identical to that of wheat RALyase.
A rice gene, OsRALyase1, encoding a product similar to wheat ribosomal RNA apurinic site specific lyase (RALyase), was isolated and expressed in vitro. An open reading frame of the gene predicted a protein of 476 amino acid residues with 75% identity to RALyase and contained an F-box-like motif in its amino terminal region. The rice gene product expressed in a wheat-germ protein expression system had the same characteristics as its wheat counterpart, cleaving a specific depurinated site of the 28S rRNA sarcin-ricin domain.
Amino Acid Motifs↗