An HP1-Like Protein is Missing from Transcriptionally Silent Micronuclei of Tetrahymena

• Published in: Proceedings of the National Academy of Sciences - PNAS 1998-11, Vol.95 (23), p.13624-13629
• Main Authors: Huang, Hui, Wiley, Emily A., Lending, Craig R., Allis, C. David
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Antibodies; Antiserum; Base Sequence; Biological Sciences; Cell Nucleus - genetics; Cell Nucleus - metabolism; Cellular biology; Chromatin; Chromobox Protein Homolog 5; Chromosomal Proteins, Non-Histone - genetics; Cloning, Molecular; DNA; Drosophila; Gels; Genes, Protozoan; Genetics; Heterochromatin; Histones; Macronucleus; Molecular Sequence Data; Peptides; Phosphorylation; Proteins; Protozoa; Repression; Sequence Alignment; Tetrahymena; Tetrahymena - genetics; Tetrahymena - metabolism; Transcription, Genetic
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.95.23.13624

We report the identification and cloning of a 28-kDa polypeptide (p28) in Tetrahymena macronuclei that shares several features with the well studied heterochromatin-associated protein HP1 from Drosophila. Notably, like HP1, p28 contains both a chromodomain and a chromoshadow domain. p28 also shares features with linker histone H1, and like H1, p28 is multiply phosphorylated, at least in part, by a proline-directed, Cdc2-type kinase. As such, p28 is referred to as Hhp1p (for H1/HP1-like protein). Hhp1p is missing from transcriptionally silent micronuclei but is enriched in heterochromatin-like chromatin bodies that presumably comprise repressed chromatin in macronuclei. These findings shed light on the evolutionary conserved nature of heterochromatin in organisms ranging from ciliates to humans and provide further evidence that HP1-like proteins are not exclusively associated with permanently silent chromosomal domains. Our data support a view that members of this family also associate with repressed states of euchromatin.