Chromosome condensation is a hallmark of mitosis in eukaryotes and is a prerequisite for faithful segregation of genetic material to daughter cells. Here we show that condensin, which is essential for assembling condensed chromosomes, helps to preclude the detrimental effects of gene transcription on mitotic condensation. ChIP-seq profiling reveals that the fission yeast condensin preferentially binds to active protein-coding genes in a transcription-dependent manner during mitosis. Pharmacological and genetic attenuation of transcription largely rescue bulk chromosome segregation defects observed in condensin mutants. We also demonstrate that condensin is associated with and reduces unwound DNA segments generated by transcription, providing a direct link between an in vitro activity of condensin and its in vivo function. The human condensin isoform condensin I also binds to unwound DNA regions at the transcription start sites of active genes, implying that our findings uncover a fundamental feature of condensin complexes.

Peroxisome proliferator-activated receptor (PPAR)-γ γ γ γ 2, a member of the nuclear hormone receptor superfamily, plays a key role in adipocyte differentiation. Its amino-terminal region carries a ligandindependent gene-activating function, AF-1, and is composed of activation as well as repression domains. We have found PPARγ γ γ γ 2 and its isoform, PPARγ γ γ γ 1, to be modified by small ubiquitin-related modifier (SUMO)-1 in vivo , at a lysine residue in the repression domain. In reporter assays, a sumoylation-defective K107R mutant of PPARγ γ γ γ 2 exhibited much stronger transactivation than the wild-type, comparable with that of a mutant deleted for the repression domain. A close inverse correlation was observed between the levels of sumoylation and transactivation by PPARγ γ γ γ 2, in analyses employing PPARγ γ γ γ 2 forms with mutations in the sumoylation motif and a dominantnegative mutant of the SUMO conjugating enzyme, Ubc9. Studies with phosphorylation-defective mutants suggested that phosphorylation at S112 of PPARγ γ γ γ 2 promotes K107 sumoylation, and this latter exerts the more potent repressive effects. The K107R mutant PPARγ γ γ γ 2, when infected into NIH3T3 cells with a viral vector, promoted differentiation into adipocytes more efficiently than the wild-type. These observations provide evidence that sumoylation is involved in negative regulation of the transactivating function of PPARγ γ γ γ 2.

MCPH1, a protein linked to primary microcephaly, directly modulates condensin II to regulate chromosome condensation and shape.

Condensin II initiates structural reorganization of duplicated chromosomes during S phase to prepare for their proper condensation and segregation in mitosis.

Although ribosomal proteins (RPs) are essential cellular constituents in all living organisms, mechanisms underlying regulation of their gene expression in mammals remain unclear. We have established that 22 out of 79 human RP genes contain sequences similar to the human DREF (DNA replication-related elementbinding factor; hDREF) binding sequence (hDRE) within 200-bp regions upstream of their transcriptional start sites. Electrophoretic gel mobility shift assays and chromatin immunoprecipitation analysis indicated that hDREF binds to hDRE-like sequences in the RP genes both in vitro and in vivo. In addition, transient luciferase assays revealed that hDRE-like sequences act as positive elements for RP gene transcription and cotransfection of an hDREF-expressing plasmid was found to stimulate RP gene promoter activity. Like that of hDREF, expression of RP genes is increased during the late G 1 to S phases, and depletion of hDREF using short hairpin RNA-mediated knockdown decreased RP gene expression and cell proliferation in normal human fibroblasts. Knockdown of the RPS6 gene also resulted in impairment of cell proliferation. These data suggest that hDREF is an important transcription factor for cell proliferation which plays roles in cell cycle-dependent regulation of a number of RP genes.Promoters of Drosophila melanogaster genes related to DNA replication, such as those for the 180-kDa catalytic subunit of DNA polymerase ␣ and proliferating cell nuclear antigen (PCNA), contain a common 8-bp palindromic sequence (5Ј-T ATCGATA-3Ј), named the DNA replication-related element (DRE) (12). These DREs are required for promoter activities both in cultured cells and in flies in vivo (41). We have purified the DRE-binding factor (DREF) from cultured Drosophila cells, consisting of an 86-kDa polypeptide homodimer specifically binding to DRE, and isolated a cDNA (12, 13). The importance of Drosophila DREF in development has been demonstrated from studies using transgenic flies (11,14,44). For example, ectopic expression of Drosophila DREF in eye imaginal disc cells behind the morphogenetic furrow, which are normally postmitotic, induced ectopic DNA synthesis and apoptosis and abolished photoreceptor specifications (11). More recently, we and Hyun et al. have succeeded in knocking down Drosophila DREF expression in various tissues (16,45). Decreased levels of DREF in developing wing and eye imaginal discs were associated with reduction in wing size with smaller cells and drastically aberrant small and rough eyes, respectively. These lines of evidence indicate that the Drosophila DRE/DREF system performs important roles in regulation of cell growth as well as cell proliferation during development.How many and what kind of genes other than those described above are under control of the Drosophila DRE/DREF system? Immunostaining of polytene chromosomes of salivary glands revealed that Drosophila DREF binds to hundreds of loci (8, 10), and recent computational analysis of core promoters in the Drosophila genome showed DRE to be...