Phosphorylation of an HP1-like Protein Regulates Heterochromatin Body Assembly for DNA Elimination

Heterochromatic loci are often assembled into higher-order heterochromatin bodies in diverse eukaryotes. However, the formation and biological roles of heterochromatin bodies are poorly understood. In the ciliated protozoan Tetrahymena, de novo heterochromatin body formation is accompanied by programmed DNA elimination. Here, we show that the heterochromatin body component Jub1p promotes heterochromatin body formation and dephosphorylation of the Heterochromatin Protein 1-like protein Pdd1p. Through the mutagenesis of the phosphorylated residues of Pdd1p, we demonstrate that Pdd1p dephosphorylation promotes the electrostatic interaction between Pdd1p and RNA in vitro and heterochromatin body formation in vivo. We therefore propose that heterochromatin body is assembled by the Pdd1p-RNA interaction. Pdd1p dephosphorylation and Jub1p are required for heterochromatin body formation and DNA elimination but not for local heterochromatin assembly, indicating that heterochromatin body plays an essential role in DNA elimination.