Interaction of the chromatin compaction-inducing domain (LR domain) of Ki-67 antigen with HP1 proteins.
BACKGROUND
The LR domain of marsupial chmadrin is defined by its C-terminal amino acid sequence, which contains several pairs of leucine (L) and arginine (R) residues. The LR domain of chmadrin causes a significant compaction of chromatin over the entire length of chromosomes when it is overproduced. The possible human homologue of chmadrin, Ki-67 antigen (pKi-67), also has a stretch of LR pairs, but with no obvious overall similarity, at its C-terminus.


RESULTS
The LR domain of human pKi-67 also induced chromatin compaction, both in human and marsupial cells. A yeast two-hybrid assay and an in vitro binding assay demonstrated that the human LR domain binds to heterochromatin protein 1 (HP1), a well-characterized molecule as a mediator of heterochromatin formation. In fixed cells stained with specific antibodies, the pKi-67 was found to be co-localized partially with HP1 at foci on chromosomes in an early G1 phase. Time-lapse observation in living cells co-expressing the fluorescently tagged proteins showed that the LR domain formed foci on chromosomes over a limited period of the cell cycle from the telophase to early G1 phase and that HP1 subsequently accumulated at these foci of the LR domain.


CONCLUSIONS
Marsupial chmadrin and human pKi-67 induce chromatin compaction across species, possibly via the interaction of its LR domain with HP1.
Kametaka
Ai
A
Department of Cell Biology and Neuroscience, Graduate School of Medicine, Osaka University, 2-2 Yamada-oka, Suita, Japan.
Takagi
Masatoshi
M
Hayakawa
Tomohiro
T
Haraguchi
Tokuko
T
Hiraoka
Yasushi
Y
Yoneda
Yoshihiro
Y
D000595:Amino Acid Sequence; D000818:Animals; D002843:Chromatin / Q000378:metabolism*; D000090266:Chromobox Protein Homolog 5; D002868:Chromosomal Proteins, Non-Histone / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D019394:Ki-67 Antigen / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008394:Marsupialia / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D020798:Two-Hybrid System Techniques
D002843:Chromatin; D002868:Chromosomal Proteins, Non-Histone; D019394:Ki-67 Antigen; D011993:Recombinant Fusion Proteins; D000090266:Chromobox Protein Homolog 5