Molecular mechanism of blue-light signal transduction in photosynthetic bacteria

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1.A transcription factor (SPB) which regulates the expression of puf-operon in Rhodobacter sphaeroides was detected by the gel-shift assay and cloned after purification.2.SPB had molecular mass of 11.5 kDa and contained a lecine-zipper motif in the N-terminal region.3.SPB was constitutively expressed and phosphorylation/dephosphorylation of SPB regulated the expression of the puf-operon of the bacterium. (phosphorylated SPB repressed the expression of the puf-operon)4.A mutant in which SPB was disrupted exhibited higher pigment content and growth rate under low-light photosynthesis than the parent, whereas the growth rate by respiration was not altered.5.The results mentioned above suggested that SPB regulated the expression of the puf-operon as a repressor.6.DNA sequenccing of the flanking region of SPB revealed that there were a two=component regulatory system upstream of SPB and three ORFs downstream of SPB.