SUMMARY We report the construction and analysis of 4,836 heterozygous diploid deletion mutants covering 98.4% of the fission yeast genome. This resource provides a powerful tool for biotechnological and eukaryotic cell biology research. Comprehensive gene dispensability comparisons with budding yeast, the first time such studies have been possible between two eukaryotes, revealed that 83% of single copy orthologues in the two yeasts had conserved dispensability. Gene dispensability differed for certain pathways between the two yeasts, including mitochondrial translation and cell cycle checkpoint control. We show that fission yeast has more essential genes than budding yeast and that essential genes are more likely than non-essential genes to be single copy, broadly conserved and to contain introns. Growth fitness analyses determined sets of haploinsufficient and haploproficient genes for fission yeast, and comparisons with budding yeast identified specific ribosomal proteins and RNA polymerase subunits, which may act more generally to regulate eukaryotic cell growth.

The positioning of the nucleosome by ATP-dependent remodellers provides the fundamental chromatin environment for the regulation of diverse cellular processes acting on the underlying DNA. Recently, genome-wide nucleosome mapping has revealed more detailed information on the chromatin-remodelling factors. Here, we report that the Schizosaccharomyces pombe CHD remodeller, Hrp3, is a global regulator that drives proper nucleosome positioning and nucleosome stability. The loss of Hrp3 resulted in nucleosome perturbation across the chromosome, and the production of antisense transcripts in the hrp3D cells emphasized the importance of nucleosome architecture for proper transcription. Notably, perturbation of the nucleosome in hrp3 deletion mutant was also associated with destabilization of the DNA-histone interaction and cell cycle-dependent alleviation of heterochromatin silencing. Furthermore, the effect of Hrp3 in the pericentric region was found to be accomplished via a physical interaction with Swi6, and appeared to cooperate with other heterochromatin factors for gene silencing. Taken together, our data indicate that a well-positioned nucleosome by Hrp3 is important for the spatial-temporal control of transcriptionassociated processes.

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The transcriptional regulation of the human telomerase reverse transcriptase (hTERT) gene is a critical step in transformation and differentiation. Human papillomavirus E2 protein inhibits cell growth in HPV-infected cells and triggers apoptosis in HeLa cells. Because E2 induces cell growth suppression and senescence, we hypothesize that the protein may modulate cellular gene expression related to these processes. In this report, we demonstrate that E2 inhibits the hTERT promoter. The mapping of the E2-responsive region of hTERT reveals that Sp1 is important for E2-mediated repression of this promoter in 293T cells. Site-directed mutagenesis data on the hTERT promoter show that E2 does not abolish E-Box-mediated transcription and represses promoter activity via the Sp1 binding site. Furthermore, chromatin immunoprecipitation assays indicate that E2 is actively recruited to the hTERT promoter region. Our findings provide novel insights into the biological function of human papillomavirus E2. Papillomavirus (PV),1 which infects mammalian cells, encodes two transcription/replication regulatory proteins (E1 and E2) in its ϳ7900-bp genome (1). Both E1 and E2 associate with host cellular proteins involved in the transcriptional regulation and DNA replication, making PV a useful model for the study of these cellular processes in mammals (2-5). The bovine PV E1 protein functions as an ATPase, DNA helicase, and a replication origin-specific binding protein initiating viral-specific DNA replication in concert with viral E2 protein (6 -11). The protein encoded by the E2 open reading frame is a regulatory factor that controls the transcription of the viral genome by host RNA polymerase II (12). PV E2 binds as a dimer to 12-bp inverted repeats (ACCN 6 GGT) present in the PV upstream regulatory region and consequently activates or represses transcription (13-15). E2 contains an NH 2 -terminal transcription activation domain and a COOH-terminal DNA-binding domain separated by a flexible hinge (16). Various regulatory proteins interact with human PV E2 to modulate E2-mediated transcription and viral replication (17-21). Recent reports (22-24) suggest that the E2 transcriptional activation function is required for the E6/E7 promoter repression. The point mutations in specific conserved sites within the bovine or human PV E2 transactivation domain that result in the loss of transcriptional activation also eliminate E6/E7 promoter repression. E2 induces senescence in HPV-positive cells via pRb-and p21-dependent pathways (25). Because E2 is associated with growth suppression and senescence, it is possible that the protein modulates cellular gene expression related to these processes.Telomeres form the ends of eukaryotic chromosomes composed of tandem arrays of telomeric repeats (5Ј-TTAGGG-3Ј in human) (reviewed in Ref. -16 E6 (39 -41). The observation that the introduction of viral E2 into HPV-infected cells inhibits telomerase activity raises the possibility of a link between hTERT expression and the E2 protein. In this study, we...

Caudal agenesis refers to the congenital malformation with the essential feature of the agenesis of the sacrococcygeal bone. It is associated with various types of spinal cord anomaly as well as with complex anomalies of genitourinary or gastrointestinal system. The wide spectrum of the disease can be attributed to its pathoembryological origin, the secondary neurulation. This review presents the definition, etiology, classification, and clinical features of the disease.