Light-regulated expression of the psbD gene family in Synechococcus sp. strain PCC 7942: evidence for the role of duplicated psbD genes in cyanobacteria.
ABSTRACT The genome of the cyanobacterium Synechococcus sp. strain PCC 7942 contains two psbD genes encoding the D2 protein of the photosystem II reaction center: psbDI, which is cotranscribed as a discistronic message with psbC (the gene encoding CP43, a chlorophyll-a binding protein), and psbDII, which is monocistronic. Northern blot analysis of psbD transcripts showed that the two genes responded differently when wild-type cells were shifted from moderate to high light intensity. Whereas psbDII transcripts increased 500% relative to unshifted control cells, psbDI-psbC transcripts remained unchanged. The beta-galactosidase activities expressed from translational fusions between the psbD genes and the Escherichia coli lacZ reporter gene displayed responses similar to those seen in the RNA. D2 protein levels in thylakoid membranes from wild-type cells increased to 250% of those of the unshifted control cells 12 h after a shift to high light intensities. In contrast, in a mutant strain (AMC016) that carries an inactive psbDII gene, D2 levels decreased by 50% under identical conditions. These results suggested that induction of psbDII gene expression by light can serve as a supplementary system for maintaining a functional photosystem II reaction center at high light intensity. This hypothesis was corroborated by mixed-culture experiments, in which AMC016 cells competed poorly with wild-type cells at high light intensity. These data suggest for the first time that differential expression of members of a cyanobacterial gene family serves to maintain a functional PSII reaction center under diverse environmental conditions.
- [show abstract] [hide abstract]
ABSTRACT: A new class of plasmid cloning vectors has been constructed with cleavage sites in a variety of translational reading phases of the promotorless lacZ gene. Fused hybrid proteins can be produced by these vectors by cloning DNA fragments containing the promoter, translation initiation site, and the amino terminal portion of a gene, all with proper orientation, into the correct translational reading frame of the lacZ gene. Enzymatically active hybrid-beta-galactosidase proteins are formed, which have amino-terminal amino acids encoded by the cloned gene segment. Another class of these vectors retains an active lac promoter and lacZ translation-initiation region, which can direct hybrid protein synthesis from DNA fragments that do not have gene initiation regions. These vectors allow transcription from the lacZ initiation region to proceed across, or to stop and restart within, an inserted fragment into the essential part of the beta-galactosidase gene. Also described is a small lacZ gene fragment (cartridge), without a plasmid replicon and without any other lac genes, which can be inserted directly into other genes to form hybrid protein fusions. Polyrestriction site sequences were easily moved into some of these vectors by incorporating drug-resistance genes that serve as markers for the selection and detection of these sequences; those markers can be easily removed afterwards.Gene 12/1983; 25(1):71-82. · 2.20 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: We have established schedules of expression during maize leaf development in light and darkness for the messenger RNAs (mRNAs) and polypeptides for ribulose 1,5-bisphosphate carboxylase (RuBPCase) subunits, phosphoenolpyruvate carboxylase (PEPCase), and the light-harvesting chlorophyll a/b-binding protein (LHCP). Levels of mRNAs were measured by hybridization with cloned probes, and proteins were measured by immunodetection on protein gel blots. The initial synthesis in leaves of all four mRNAs follows a light-independent schedule; illumination influences only the level to which each mRNA accumulates. The synthesis of RuBPCase small and large subunits and of PEPCase polypeptides also follows a light-independent schedule which is modified quantitatively by light. However, the accumulation of LHCP polypeptides absolutely requires illumination. The accumulation of each protein closely follows the accumulation of its mRNA during growth in light. Higher ratios of PEPCase and RuBPCase protein to mRNA occur during dark growth.The Journal of Cell Biology 03/1984; 98(2):558-64. · 10.82 Impact Factor