Biomedical subjects

Ee Sin Chen

Publications and source records attributed to Ee Sin Chen.

4 recordsLinked to original sources

PubMed2005

Comprehensive analysis of heterochromatin- and RNAi-mediated epigenetic control of the fission yeast genome.

The organization of eukaryotic genomes into distinct structural and functional domains is important for the regulation and transduction of genetic information. Here, we investigated heterochromatin and euchromatin profiles of the entire fission yeast genome and explored the role of RNA interference (RNAi) in genome organization. Histone H3 methylated at Lys4, which defines euchromatin, was not only distributed across most of the chromosomal landscape but was also present at the centromere core, the site of kinetochore assembly. In contrast, histone H3 methylated at Lys9 and its interacting protein Swi6/HP1, which define heterochromatin, coated extended domains associated with a variety of repeat elements and small islands corresponding to meiotic genes. Notably, RNAi components were distributed throughout all these heterochromatin domains, and their localization depended on Clr4/Suv39h histone methyltransferase. Sequencing of small interfering RNAs (siRNAs) associated with the RITS RNAi effector complex identified hot spots of siRNAs, which mapped to a diverse array of elements in these RNAi-heterochromatin domains. We found that Clr4/Suv39h predominantly silenced repeat elements whose derived transcripts, transcribed mainly by RNA polymerase II, serve as a source for siRNAs. Our analyses also uncover an important role for the RNAi machinery in maintaining genomic integrity.

DNA Methylation↗

PubMed2004

Cti1/C1D interacts with condensin SMC hinge and supports the DNA repair function of condensin.

Condensin is a conserved five-subunit complex containing two SMC (structural maintenance of chromosomes) and three non-SMC subunits and plays a major role in mitotic chromosome condensation. Condensin also acts in interphase and is required for DNA repair and replication checkpoint control. We attempted to study the function of the condensin in greater detail by means of the isolation of interacting proteins with the two-hybrid system. Using the hinge domain of Cut3/SMC4 as bait, we found one Cut three-interacting (Cti) 14-kDa nuclear protein, Cti1. GST pull-down assay and immunoprecipitation supported physical interaction between Cti1 and condensin. Cti1 is similar to human C1D, which associates tightly with genomic DNA and functions to activate DNA protein kinase. SpC1D is essential for viability. The null mutant could germinate but arrest after replication, indicating that it is required for interphase growth. Importantly, an elevated dosage of spC1D suppressed the temperature, UV irradiation, and hydroxyurea sensitivity of the mutant of Cnd2, a non-SMC subunit of condensin. Upon exposure to hydroxyurea, spC1D accumulated on the nuclear chromatin, and the fraction of spC1D that was chromatin-bound increased. Cti1 is the first example of the protein that interacts with the hinge domain of SMC. Cti1 may have a supporting role for the DNA repair function of condensin.

Adenosine Triphosphatases↗

PubMed2003

A cell cycle-regulated GATA factor promotes centromeric localization of CENP-A in fission yeast.

CENP-A, the centromere-specific histone H3 variant, plays a crucial role in organizing kinetochore chromatin for precise chromosome segregation. We have isolated Ams2, a Daxx-like motif-containing GATA factor, and histone H4, as multicopy suppressors of cnp1-1, an S. pombe CENP-A mutant. While depletion of Ams2 results in the reduction of CENP-A binding to the centromere and chromosome missegregation, increasing its dosage restores association of a CENP-A mutant protein with centromeres. Conversely, overexpression of CENP-A or histone H4 suppresses an ams2 disruptant. The intracellular amount of Ams2 thus affects centromeric nucleosomal constituents. Ams2 is abundant in S phase and associates with chromatin, including the central centromeres through binding to GATA-core sequences. Ams2 is thus a cell cycle-regulated GATA factor that is required for centromere function.

Amino Acid Motifs↗

PubMedDate not supplied

Does a GATA factor make the bed for centromeric nucleosomes?

CENP-A is an evolutionarily conserved, centromere-specific histone H3 variant. It remains a great mystery how CENP-A is correctly incorporated into the centromere, a restricted chromosomal region, despite the presence of an overwhelming amount of histone H3. We identified a cell cycle-regulated GATA factor, Ams2, as a component of the CENP-A localization pathway in fission yeast. Unexpectedly, this putative transcription factor, which belongs to a protein family containing members that remodel nucleosomes, appeared to bind to and function at the central region of the centromere. Although the centromere has in general been considered transcriptionally inactive, fission yeast's outer centromeric region has recently been shown to encode non-translated snRNAs that are involved in heterochromatin formation. Transcription factors such as Ams2 may directly transcribe some unidentified non-translated centromeric RNAs. Transcription and/or remodeling of the nucleosomes at the centromeres may be important for the precise incorporation of CENP-A in fission yeast.

Autoantigens↗