|
|
|
|
|
|
The Reaction Center H Subunit Is Not Required for High Levels of Light-Harvesting Complex 1 in Rhodospirillum rubrum Mutants. Domenico Lupo, 2004.The gene (puhA) encoding the H subunit of the reaction center (RC) was deleted by site-directed interposon mutagenesis by using a kanamycin resistance cassette lacking transcriptional terminators to eliminate polar effects in both the wild-type strain Rhodospirillum rubrum S1 and the carotenoid-less strain R . rubrum G9 . The puhA interposon mutants were incapable of photoheterotrophic growth but grew normally under aerobic chemoheterotrophic conditions . Absorption spectroscopy and sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the RCs were absent . In minimal medium and also in modified medium containing succinate and fructose, the light-harvesting 1 complex (LH1) levels of the S1-derived mutants were about 70 to 100% of the wild-type levels in the same media . The correct assembly of LH1 in the membrane and the pigment-pigment interaction were confirmed by near-infrared circular dichroism spectroscopy . LH1 formation was almost absent when the carotenoid-less G9-derived puhA mutants were grown in standard minimal medium, suggesting that carotenoids may stabilize LH1 . In the fructose-containing medium, however, the LH1 levels of the G9 mutants were 70 to 100% of the parental strain levels . Electron micrographs of thin sections of R . rubrum revealed photosynthetic membranes in all mutants grown in succinate-fructose medium . These studies indicate that the H subunit of the RC is necessary neither for maximal formation of LH1 nor for photosynthetic membrane formation but is essential for functional RC assembly . Control of Photosynthetic and High-Light-Responsive Genes by the Histidine Kinase DspA: Negative and Positive Regulation and Interactions between Signal Transduction Pathways. Hui-Yi Hsiao, 2004.We have deleted a gene for a sensor histidine kinase, dspA (or hik33), in the cyanobacterium Synechocystis sp . strain PCC6803 . In low and moderate light, the mutant grew slowly under photoautotrophic conditions, with a doubling time of  40
h, and had severely reduced photosynthetic oxygen evolution . When the
mutant was maintained in low or moderate light in the presence of
glucose, its growth rate was only somewhat lower than that of
wild-type cells . However, the mutant was light sensitive and rapidly
died in high light . Furthermore, levels of many transcripts encoding
genes associated with photosynthesis were altered in the mutant
relative to wild-type Synechocystis sp . strain PCC6803 both in
low light and following exposure to high light . There was
constitutive expression of several high-light-inducible genes,
including hli, psbAIII, and gpx2; there was
little increased accumulation of sodB mRNA in high light; and
the cells failed to accumulate cpcBA and psaAB mRNAs in
low light in the presence of glucose, although a normal decline in
the levels of these mRNAs was observed during exposure to high light .
These results suggest that DspA is involved in controlling sets of
photosynthetic and high-light-responsive genes, either directly or
indirectly . These and other results, some of which are presented in a
companion paper (C.-J . Tu, J . Shrager, R . Burnap, B . L . Postier, and
A . R . Grossman, J . Bacteriol . 186:3889-3902, 2004), suggest that DspA
acts as a global regulator that helps coordinate cellular metabolism
with growth limitations imposed by environmental conditions .
Galactose and Lactose Genes from the Galactose-Positive Bacterium Streptococcus salivarius and the Phylogenetically Related Galactose-Negative Bacterium Streptococcus thermophilus: Organization, Sequence, Transcription, and Activity of the gal Gene Products. Katy Vaillancourt, 2002.Streptococcus salivarius is a lactose- and galactose-positive bacterium that is phylogenetically closely related to Streptococcus thermophilus, a bacterium that metabolizes lactose but not galactose . In this paper, we report a comparative characterization of the S . salivarius and S . thermophilus gal-lac gene clusters . The clusters have the same organization with the order galR (codes for a transcriptional regulator and is transcribed in the opposite direction), galK (galactokinase), galT (galactose-1-P uridylyltransferase), galE (UDP-glucose 4-epimerase), galM (galactose mutarotase), lacS (lactose transporter), and lacZ (ß-galactosidase) . An analysis of the nucleotide sequence as well as Northern blotting and primer extension experiments revealed the presence of four promoters located upstream from galR, the gal operon, galM, and the lac operon of S . salivarius . Putative promoters with virtually identical nucleotide sequences were found at the same positions in the S . thermophilus gal-lac gene cluster . An additional putative internal promoter at the 3' end of galT was found in S . thermophilus but not in S . salivarius . The results clearly indicated that the gal-lac gene cluster was efficiently transcribed in both species . The Shine-Dalgarno sequences of galT and galE were identical in both species, whereas the ribosome binding site of S . thermophilus galK differed from that of S . salivarius by two nucleotides, suggesting that the S . thermophilus galK gene might be poorly translated . This was confirmed by measurements of enzyme activities .
|
© 2005
Transgalactic Ltd (manufacturer of Bioscreen C software) |
Privacy Statement | P.O. Box
1393, 00101 Helsinki, Finland,
Last modified: May 25, 2005
| ||||||
