In Synechocystis sp. PCC 6803, gene sll1384 encodes a protein with a DnaJ domain at its N-terminal portion and a TPR domain at the C-terminal portion. An sll1384 mutant shows no difference from the wild type in adaptation to different temperatures, but almost completely loses its capability of phototactic movement. After complementation with sll1384, the mutant regains the phototaxis. As shown with electron microscopy, on the cell surface, mutant cells have pili that appear to be the same as that of the wild type. Also, the transformation efficiency remains unchanged in the mutant. It is postulated that Sll1384 regulates phototaxis of Synechocystis through protein-protein interaction. It is the first DnaJ-like protein gene identified in a cyanobacterium for a role in phototaxis.
Phosphohexomutases catalyze the interconversion between hexose-6-phosphate and hexose-1-phosphate and play important roles in polysaccharide synthesis.In Synechocystis sp.PCC 6803,sll0726 is predicted to encode PGM(phosphoglucomutase),slr1334is predicted to encode a PGM/PMM(phosphomannomutase)bifunction enzyme.In comparison to the wild type,a sll0726-null mutant showed 3.4%PGM activity but 45%–69%glycogen content.Down-regulation of slr1334,an essential gene,by using a copper regulated promoter further decreased the PGM activity in the sll0726::KmrPpetE-slr1334 double mutant to 0.3%of the wild type level.However,the glycogen content was not further decreased in parallel.In vitro,recombinant Sll0726 or Slr1334 showed predicted enzyme activities.Our results indicate that a relatively high level of glycogen can be maintained in Synechocystis mutants with low levels of PGM activity.The high PGM activity in the cyanobacterium may be required for turnover of glycogen or synthesis of other polysaccharides or oligosaccharides.
In bacteria, FtsH proteases are involved in quality maintenance of membrane proteins and cellular regulation at the level of protein stability. Among the 4 predicted ftsH genes in the cyanobacterium Anabaena sp. PCC 7120, namely alr1262, all3642, all4776 and all4936, at least the first two showed reduced transcription in specialized N2-fixing cells called heterocysts. In contrast, the transcription of a small internal antisense RNA (aftsH) of all3642 was up-regulated in heterocysts. Overexpression of the antisense RNA suppressed the expression of all3642, alr1262 and all4776. Control of promoter and modulation by antisense RNA may both contribute to gene regulation in heterocysts of filamentous cyanobacteria.
GONG YangMin & XU XuDong State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China
In the cyanobacterium Synechocystis 6803, rbp3, a type-II RNA-binding protein gene, is slightly induced by temperature downshift. An rbp3 mutant shows significant reduction in total polyunsaturated fatty acids (PUFA) in membrane lipids. However, the reduction in PUFA has not attained the extent that would significantly affect the growth of the mutant at low temperature. Transcripts of fatty acid desaturase genes desA, desB and desD, and ccr-1, a gene required for growth at 15°C, are significantly reduced in the mutant relative to the wild type, while transcripts of rbp1 (RNA-binding protein 1) and crhR (RNA helicase Light) are not affected. Rbp3 may directly or indirectly affect mRNA levels of certain genes.
