Abstract
Casein kinase 2 (CK2) is known as a transcriptional regulator in both animals and yeasts. In mustard, CK2-like protein was detected as a component of the chloroplast transcription apparatus. In Arabidopsis, four CK2-like kinases are encoded in the nuclear genome. One of them (At2g23070) has a putative transit sequence at N-terninus, and was indeed targeted to chloroplasts, and we named it AtcpCK2. RNA-gel blot analysis indicated that the level of AtcpCK2 transcript was similar in both light- and dark-grown seedlings. The incorporation of UTP was inhibited by AtcpCK2 in chloroplast nucleoids. The fluorescence intensity of DAPI-stained nucleoids was decreased by the addition of AtcpCK2, suggesting compaction of chloroplast DNA by phosphorylation of nucleoid protein. We suggest that AtcpCK2 regulates the transcriptional activity of chloroplast nucleoids through changes in nucleoids conformation.
