A nuclear mutation conferring thiostrepton resistance in Chlamydomonas reinhardtii affects a chloroplast ribosomal protein related to Escherichia coli ribosomal protein L11

The rice nuclear gene WLP1 encoding a chloroplast ribosome L13 protein is needed for chloroplast development in rice grown under low temperature conditions

Plastidial ribosome proteins (PRPs) form the major component of the plastidial ribosome. Here we describe a rice mutant named wlp1 (white leaf and panicles 1) selected from a population of tissue culture regenerants. The early seedling leaves of the mutant were albino, as was the immature panicle at heading, and the phenotype was more strongly expressed in plants exposed to low temperature conditions. Changes in the leaf pigmentation of the mutant were due to altered chlorophyll content and chloroplast development. Positional cloning of WLP1, followed by complementation and knock-down experiments, showed that it encodes a 50S ribosome L13 protein. The WLP1 protein localized to the chloroplast. WLP1 was mainly transcribed in green tissues and particularly abundantly in the early seedling leaves. In addition, the expression level of WLP1 was induced by the low temperature. The transcription pattern of a number of genes involved in plastidial transcription/translation and in photosynthesis was altered in the wlp1 mutants. These results reveal that WLP1 is required for normal chloroplast development, especially under low temperature conditions. This is the first report on the function of PRPs in rice.

Thiostrepton-resistant mutants of Thermus thermophilus

Ribosomal protein L11 and its associated binding site on 23S rRNA together comprise one of the principle components that mediate interactions of translation factors with the ribosome. This site is also the target of the antibiotic thiostrepton, which has been proposed to act by preventing important structural transitions that occur in this region of the ribosome during protein synthesis. Here, we describe the isolation and characterization of spontaneous thiostrepton-resistant mutants of the extreme thermophile, Thermus thermophilus. All mutations were found at conserved positions in the flexible N-terminal domain of L11 or at conserved positions in the L11-binding site of 23S rRNA. A number of the mutant ribosomes were affected in in vitro EF-G-dependent GTP hydrolysis but all showed resistance to thiostrepton at levels ranging from high to moderate. Structure probing revealed that some of the mutations in L11 result in enhanced reactivity of adjacent rRNA bases to chemical probes, suggesting a more open conformation of this region. These data suggest that increased flexibility of the factor binding site results in resistance to thiostrepton by counteracting the conformation-stabilizing effect of the antibiotic.

Chlamydomonas DIP13 and human NA14: a new class of proteins associated with microtubule structures is involved in cell division

We have cloned and characterized a single copy C. reinhardtii gene containing an open reading frame of 333 nucleotides encoding a 12.7 kDa protein. The novel protein, DIP13, exhibits 60% identity with two mammalian proteins, human NA14 and an unnamed mouse protein. Homologous sequences are also present in several protozoan, trematode and fish genomes, but no homologs have been found in the completed genomes of yeast, Drosophila, C. elegans and A. thaliana. By using a specific antibody we have localized DIP13 to microtubule structures, namely basal bodies, flagellar axonemes and cytoplasmic microtubules. Anti-DIP13 antibody also specifically recognized human NA14 by immunofluorescence and stained basal bodies and flagella of human sperm cells as well as the centrosome of HeLa cells. Expression of the DIP13 open reading frame in antisense orientation in Chlamydomonas resulted in multinucleate, multiflagellate cells, which suggests a role for this protein in ensuring proper cell division. Thus, DIP13/NA14 could represent the founding members of a new class of highly conserved proteins that are associated with microtubule structures.

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.

Differential display of vincristine-resistance-related genes in gastric cancer SGC7901 cell

AIM: To isolate and clone the vincristine-resistine-related genes in gastric cancer SGC7901 cell line and to clarify the multidrug-resistant molecular mechanism of gastric cancer cells.

METHODS: The modified differential-display polymerase chain reaction (DD-PCR) was used to examine the differences in the mRNA composition of Vincristine-resistant gastric cancer SGC 7901 cells (SGC7901/VCR), induced by vincristine sulfate versus SGC7901 cells. The differentially expressed cDNA fragments were confirmed by reverseNorthern analysis, sequencing, BLAST analysis and Northern bolt analysis.

RESULTS: DD-PCR identified that 54 cDNA fragments were preferentially expressed in SGC 7901/VCR cells. When these cDNA fragments were analyzed by reverse Northern blot, 20 were reproducibly expressed at a high level in SGC7901/VCR. Sequencing and BLAST analysis revealed that seven of the genes were known genes: ADP-ribosylation factor 4, Cytochrome oxidase subunit II, Ss-A/Ro ribonucleoprtein autoantigen 60kd subunit, ribosomal protein S13, galaectin-8 gene, oligophrenin 1 mRNA, ribosomal protein L23 mRNA; thirteen of the genes were unknown genes. The length and abundance of the four unknown genes mRNA were further confirmed by Northern blot analysis.

CONCLUSION: The twenty differential known and unknown genes may be related to the vincristine-resistant mechanism in human gastric cancer SGC7901 cell line.

Knock-out of the plastid ribosomal protein L11 in Arabidopsis: effects on mRNA translation and photosynthesis

The prpl11-1 mutant of Arabidopsis thaliana was identified among a collection of T-DNA tagged lines on the basis of a decrease in the effective quantum yield of photosystem II. The mutation responsible was localized to Prpl11, a single-copy nuclear gene that encodes PRPL11, a component of the large subunit of the plastid ribosome. The amino acid sequence of Arabidopsis PRPL11 is very similar to those of L11 proteins from spinach and prokaryotes. In the prpl11-1 mutant, photosensitivity and chlorophyll fluorescence parameters are significantly altered owing to changes in the levels of thylakoid protein complexes and stromal proteins. The abundance of most plastome transcripts examined, such as those of genes coding for the photosystem II core complex and RbcL, is not decreased. Plastid ribosomal RNA accumulates in wild-type amounts, and the assembly of plastid polysomes on the transcripts of the rbcL, psbA and psbE genes remains mainly unchanged in mutant plants, indicating that lack of PRPL11 affects neither the abundance of plastid ribosomes nor their assembly into polysomes. However, in vivo translation assays demonstrate that the rate of translation of the large subunit of Rubisco (RbcL) is significantly reduced in prpl11-1 plastids. Our data suggest a major role for PRPL11 in plastid ribosome activity per se, consistent with its location near the GTPase-binding centre of the chloroplast 50S ribosomal subunit. Additional effects of the mutation, including the pale green colour of the leaves and a drastic reduction in growth rate under greenhouse conditions, are compatible with reduced levels of protein synthesis in plastids.

Erythromycin resistance peptides selected from random peptide libraries

Translation of a 5-codon mini-gene encoded in Escherichia coli 23 S rRNA was previously shown to render cells resistant to erythromycin (Tenson, T., DeBlasio, A., and Mankin, A. S. (1996) Proc. Natl. Acad. Sci. U. S. A. 93, 5641-5646). Erythromycin resistance was mediated by a specific interaction of the 23 S rRNA-encoded pentapeptide with the ribosome. In the present study, peptides conferring erythromycin resistance were selected from in vivo expressed random peptide libraries to study structural features important for peptide activity. Screening of a 21-codon mini-gene library (the general structure ATG (NNN)20 TAA) demonstrated that only short peptides (3-6 amino acids long) conferred erythromycin resistance. Sequence comparison of erythromycin resistance peptides isolated from the 5-codon library (ATG (NNN)4 TAA) revealed a strong preference for leucine or isoleucine as a third amino acid and a hydrophobic amino acid at the C terminus of the peptide. When tested against other antibiotics, erythromycin resistance peptides rendered cells resistant to other macrolides, oleandomycin and spiramycin, but not to chloramphenicol or clindamycin. Defining the consensus amino acid sequence of erythromycin resistance peptides provided insights into a possible mode of peptide action and the nature of the peptide binding site on the ribosome.