Sister chromatid cohesion is essential for cell viability. We have isolated a novel temperature-sensitive lethal mutant named eso1-H17 that displays spindle assembly checkpoint-dependent mitotic delay and abnormal chromosome segregation. At the permissive temperature, the eso1-H17 mutant shows mild sensitivity to UV irradiation and DNA-damaging chemicals. At the nonpermissive temperature, the mutant is arrested in M phase with a viability loss due to a failure to establish sister chromatid cohesion during S phase. The lethal M-phase arrest phenotype, however, is suppressed by inactivation of a spindle checkpoint. The eso1 ؉ gene is not essential for the onset and progression of DNA replication but has remarkable genetic interactions with those genes regulating the G 1 -S transition and DNA replication. The N-terminal two-thirds of Eso1p is highly homologous to DNA polymerase of budding yeast and humans, and the C-terminal one-third is homologous to budding yeast Eco1p (also called Ctf7p), which is required for the establishment of sister chromatid cohesion. Deletion analysis and determination of the mutation site reveal that the function of the Eco1p/Ctf7p-homologous domain is necessary and sufficient for sister chromatid cohesion. On the other hand, deletion of the DNA polymerase domain in Eso1p increases sensitivity to UV irradiation. These results indicate that Eso1p plays a dual role during DNA replication. The C-terminal region acts to establish sister chromatid cohesion, and the N-terminal region presumably catalyzes translesion DNA synthesis when template DNA contains lesions that block regular DNA replication.Virtually all eukaryotic cells propagate through a process called the cell cycle that consists of four distinct phases, G 1 , S, G 2 , and M, whose principal role is to carry out duplication of the chromosomes and subsequent faithful distribution into daughter cells. Commitment to the initiation of the cell cycle is made at a point in late G 1 phase called start or restriction point. In the fission yeast, Schizosaccharomyces pombe, passage through start requires the execution of at least two regulatory systems, Res-Cdc10-Rep (Res1p-Cdc10p and Res2p-Cdc10p-Rep2p) transcriptional factor complexes and Cdc2p-Cig2p/Cyc17p cyclin-dependent kinase complex (reviewed in references 37 and 54). Res-Cdc10-Rep complexes activate cell cycle start-specific transcription genes, which contain a cis regulatory element called the MluI cell cycle box. One of those target genes is cdc18 ϩ , whose product is a key component of the preinitiation form of origin replication complex and plays a crucial role in loading origins with the replication machinery including DNA polymerases in cooperation with minichromosome maintenance proteins (reviewed in reference 35). Cdc2p-Cig2p activity is also required for origin firing, but its critical target(s) has not been identified yet. These initiation factors and replication factors are highly conserved throughout eukaryotes.In order to ensure faithful transmission of the duplicated c...

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Sister chromatid cohesion is essential for cell viability. We have isolated a novel temperature-sensitive lethal mutant named eso1-H17 that displays spindle assembly checkpoint-dependent mitotic delay and abnormal chromosome segregation. At the permissive temperature, the eso1-H17 mutant shows mild sensitivity to UV irradiation and DNA-damaging chemicals. At the nonpermissive temperature, the mutant is arrested in M phase with a viability loss due to a failure to establish sister chromatid cohesion during S phase. The lethal M-phase arrest phenotype, however, is suppressed by inactivation of a spindle checkpoint. The eso1 ؉ gene is not essential for the onset and progression of DNA replication but has remarkable genetic interactions with those genes regulating the G 1 -S transition and DNA replication. The N-terminal two-thirds of Eso1p is highly homologous to DNA polymerase of budding yeast and humans, and the C-terminal one-third is homologous to budding yeast Eco1p (also called Ctf7p), which is required for the establishment of sister chromatid cohesion. Deletion analysis and determination of the mutation site reveal that the function of the Eco1p/Ctf7phomologous domain is necessary and sufficient for sister chromatid cohesion. On the other hand, deletion of the DNA polymerase domain in Eso1p increases sensitivity to UV irradiation. These results indicate that Eso1p plays a dual role during DNA replication. The C-terminal region acts to establish sister chromatid cohesion, and the N-terminal region presumably catalyzes translesion DNA synthesis when template DNA contains lesions that block regular DNA replication.

As a first step m the mvesttgatton of the reconstttutton of sterotd hormone receptor systems, we studied the reconstttutton of 9 S estrogen receptor

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