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  • 1
    Electronic Resource
    Electronic Resource
    dr and spr/sr mutations of Chlamydomonas reinhardtii affecting D1 protein function and synthesis define two independent steps leading to chronic photoinhibition and confer differential fitness (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 20 (1997), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The effects of introduced chloroplast gene mutations affecting D1 synthesis, turnover and function on photosynthesis, growth and competitive ability were examined in autotrophic cultures of Chlamydomonas reinhardtii (Chlorophyta) adapted to low or high irradiance. Few discernible effects were evident when the mutants were grown in low light (LL, 70 μmol m−2 s−1). The herbicide-resistant psbA mutation Ser264→ Ala (dr) slowed electron transfer and accelerated D1 degradation in cells grown under high light (HL, 600 μmol m−2 s−1). The maximum rate of light-and CO2-saturated photosynthesis, cell growth rate and competitive ability in the dr mutant were reduced compared to wild type under HL. However, the wild-type rate of D1 synthesis in dr was adequate to compensate for accelerated D1 degradation. 16S rRNA mutations conferring resistance to streptomycin and spectinomycin (spr/sr) that altered chloroplast ribosome structure and assembly were used to inhibit chloroplast protein synthesis. In spr/sr cells grown under HL, D1 synthesis was reduced by 40–60% compared to wild type and D1 degradation was accelerated, leading to a 4-fold reduction in D1 pool size. The reduced D1 levels were accompanied by an elevation of Fo and a decline in Fv/Fm, quantum yield and maximum rate of CO2-saturated photosynthesis. Chemostat experiments showed that the growth rate and competitive ability of spr/sr were reduced against both wild type and dr.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.1997.d01-143.x
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  • 2
    Electronic Resource
    Electronic Resource
    Shine-Dalgarno-like sequences are not required for translation of chloroplast mRNAs in Chlamydomonas reinhardtii chloroplasts or in Escherichia coli (1998)
    Springer
    Molecular genetics and genomics 257 (1998), S. 271-282 
    Details
    ISSN: 1617-4623
    Keywords: Key wordsChlamydomonas ; Translational control ; Chloroplast genetics ; Shine-Dalgarno sequence ; Chloroplast reporter genes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Initiation of translation in Escherichia coli and related eubacteria involves well-defined interactions between a conserved Shine-Dalgarno (SD) sequence immediately upstream of the initiation codon in the mRNA leader and an equally conserved anti-SD sequence at the 3′ end of the 16S rRNA. SD-like sequences found in the leaders of many, but not all, mRNAs from cyanobacteria and chloroplasts are hypervariable in location, size, and base composition compared to those in E. coli, while anti-SD sequences in the respective 16S rRNAs remain highly conserved. We have examined the function of the SD-like sequences found in the leaders of four chloroplast genes of the green alga Chlamydomonas reinhardtii using replacement mutagenesis to eliminate complementarity with the anti-SD sequences and insertion of canonical SD sequences (GGAGG) at positions −9 to −5 relative to the initiation codon. Promoter-leader regions of the atpB, atpE, rps4, and rps7 genes representing the diversity of chloroplast SD-like sequences were fused to aadA and uidA reporter genes encoding spectinomycin resistance and GUS activity respectively. Analysis of chloroplast transformants of C. reinhardtii and transformants of E. coli carrying the wild-type and mutant reporter constructs revealed that mutagenic replacement of the putative SD sequences had no effect on the expression of either the aadA or uidA reporter genes. Chloroplast transformants with the canonical SD sequence also showed no differences in reporter gene expression, whereas expression of the reporter genes was increased by 10 to 30% in the E. coli transformants. Collectively our results suggest that even though SD-dependent initiation predominates in E. coli, this bacterium also has the capacity to initiate translation by an SD-independent mechanism. In contrast, plant chloroplasts, and very probably their cyanobacterial ancestors, appear to have adopted the SD-independent mechanism for translational initiation of most mRNAs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004380050648
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    Paper (German National Licenses)
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