Detection and localization of a chloroplast-encoded HU-like protein that organizes chloroplast nucleoids.
Chloroplast DNA (cpDNA) is packed into discrete structures called chloroplast nucleoids (cp-nucleoids). The structure of cpDNA is thought to be important for its maintenance and regulation. In bacteria and mitochondria, histone-like proteins (such as HU and Abf2, respectively) are abundant and play important roles in DNA organization. However, a primary structural protein has yet to be found in cp-nucleoids. Here, we identified an abundant DNA binding protein from isolated cp-nucleoids of the primitive red alga Cyanidioschyzon merolae. The purified protein had sequence homology with the bacterial histone-like protein HU, and it complemented HU-lacking Escherichia coli mutants. The protein, called HC (histone-like protein of chloroplast), was encoded by a single gene (CmhupA) in the C. merolae chloroplast genome. Using immunofluorescence and immunoelectron microscopy, we demonstrated that HC was distributed uniformly throughout the entire cp-nucleoid. The protein was expressed constitutively throughout the cell and the chloroplast division cycle, and it was able to condense DNA. These results indicate that HC, a bacteria-derived histone-like protein, primarily organizes cpDNA into the nucleoid.
Department of Biological Science, Graduate School of Science, University of Tokyo, Tokyo 113-0033, Japan. tamaki@biol.s.u-tokyo.ac.jp
Tamaki
T
Kobayashi
Manabu
M
Takahara
Shin-ya
SY
Miyagishima
Haruko
H
Kuroiwa
Narie
N
Sasaki
Niji
N
Ohta
Motomichi
M
Matsuzaki
Tsuneyoshi
T
Kuroiwa
D020418:Algal Proteins / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics; D002736:Chloroplasts / Q000378:metabolism*; D018742:DNA, Chloroplast / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D005816:Genetic Complementation Test; D015151:Immunoblotting; D008969:Molecular Sequence Data; D009154:Mutation; D000461:Rhodophyta / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
C072843:ABF2 protein, S cerevisiae; D020418:Algal Proteins; D001426:Bacterial Proteins; D018742:DNA, Chloroplast; D004268:DNA-Binding Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; C040330:histone-like protein HU, bacteria