Phosphorylation by protein kinase CKII modulates the DNA-binding activity of a chloroplast nucleoid-associated protein.
Plastid DNA, like bacterial and mitochondrial DNA, is organized into protein-DNA complexes called nucleoids. Plastid nucleoids are believed to be associated with the inner envelope in developing plastids and the thylakoid membranes in mature chloroplasts, but the mechanism for this localization is unknown. MFP1 is a DNA-binding, coiled-coil protein associated with the thylakoid membranes of mature chloroplasts. It is also a component of nucleoids, suggesting a function at the interface of the chloroplast genome and the photosynthetic membranes. Several thylakoid proteins are phosphorylated by a protein kinase CKII-like activity and the alpha subunit of a chloroplast-located CKII has recently been identified as a component of the chloroplast transcription complex. Here, we show evidence for the phosphorylation of MFP1 in purified chloroplasts from tobacco (Nicotiana tabacum L.). We demonstrate that the DNA-binding domain of MFP1 is a substrate for CKII and that phosphorylation by CKII inhibits DNA binding. Using site-directed mutagenesis, we identify a conserved twin CKII site in the DNA-binding domain that is required for the inhibition of DNA binding. Phosphorylation of MFP1 by chloroplast CKII as a possible means to modulate its DNA-binding activity is discussed.
Plant Biotechnology Center and Department of Plant Biology, The Ohio State University, 244 Rightmire Hall, 1060 Carmack Road, Columbus, OH 43210-1002, USA.
Sun Yong
SY
Jeong
Nancy
N
Peffer
Iris
I
Meier
D000595:Amino Acid Sequence; D047390:Casein Kinase II; D002736:Chloroplasts / Q000201:enzymology* / Q000378:metabolism; D017124:Conserved Sequence; D018742:DNA, Chloroplast / Q000235:genetics / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D036961:Matrix Attachment Region Binding Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D020524:Thylakoids / Q000201:enzymology / Q000378:metabolism; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism*
D018742:DNA, Chloroplast; D036961:Matrix Attachment Region Binding Proteins; D010940:Plant Proteins; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases