We have sequenced and annotated the genome of ®ssion yeast (Schizosaccharomyces pombe), which contains the smallest number of protein-coding genes yet recorded for a eukaryote: 4,824. The centromeres are between 35 and 110 kilobases (kb) and contain related repeats including a highly conserved 1.8-kb element. Regions upstream of genes are longer than in budding yeast (Saccharomyces cerevisiae), possibly re¯ecting more-extended control regions. Some 43% of the genes contain introns, of which there are 4,730. Fifty genes have signi®cant similarity with human disease genes; half of these are cancer related. We identify highly conserved genes important for eukaryotic cell organization including those required for the cytoskeleton, compartmentation, cell-cycle control, proteolysis, protein phosphorylation and RNA splicing. These genes may have originated with the appearance of eukaryotic life. Few similarly conserved genes that are important for multicellular organization were identi®ed, suggesting that the transition from prokaryotes to eukaryotes required more new genes than did the transition from unicellular to multicellular organization.We report here the completion of the fully annotated genome sequence of the simple eukaryote Schizosaccharomyces pombe, a ®ssion yeast. It becomes the sixth eukaryotic genome to be sequenced, following Saccharomyces cerevisiae 1 , Caenorhabditis elegans 2 , Drosophila melanogaster 3 , Arabidopsis thaliana 4 and Homo sapiens 5,6 . The entire sequence of the unique regions of the three chromosomes is complete, with gaps in the centromeric regions of about 40 kb, and about 260 kb in the telomeric regions. The completion of this sequence, the availability of sophisticated research methodologies, and the expanding community working on S. pombe, will accelerate the use of S. pombe for functional and comparative studies of eukaryotic cell processes.

Base pairing between U2 snRNA and the branchpoint sequence (BPS) is essential for pre-mRNA splicing. Because the metazoan BPS is short and highly degenerate, this interaction alone is insufficient for specific binding of U2 snRNP. The splicing factor U2AF binds to the pyrimidine tract at the 3 splice site in the earliest spliceosomal complex, E, and is essential for U2 snRNP binding in the spliceosomal complex A. We show that the U2 snRNP protein SAP 155 UV cross-links to pre-mRNA on both sides of the BPS in the A complex. SAP 155's downstream cross-linking site is immediately adjacent to the U2AF binding site, and the two proteins interact directly in protein-protein interaction assays. Using UV cross-linking, together with functional analyses of pre-mRNAs containing duplicated BPSs, we show a direct correlation between BPS selection and UV cross-linking of SAP 155 on both sides of the BPS. Together, our data are consistent with a model in which U2AF binds to the pyrimidine tract in the E complex and then interacts with SAP 155 to recruit U2 snRNP to the BPS.The pre-mRNA splicing reaction is carried out with extreme precision in order to generate mRNAs that encode functional proteins. The accuracy of splicing depends on multiple sequence elements located at the 5Ј and 3Ј splice sites, at the branch site, and within exons. Networks of RNA-RNA, RNAprotein, and protein-protein interactions involving each of these sequence elements contribute to the specificity of splicing. Additional specificity is derived from the recognition of each sequence element multiple times prior to the two catalytic steps of splicing. These successive recognition events occur as the spliceosomal complexes E, A, B, and C assemble on premRNA in a stepwise pathway (for reviews, see references 17, 25, and 32).One of the critical sequence elements in the intron is the branchpoint sequence (BPS). This element contains an adenosine that functions as the nucleophile for catalytic step I of splicing. Despite its key role in splicing, the BPS is weakly conserved in metazoans, and additional elements are required for BPS recognition. The most important of these is the pyrimidine tract located immediately downstream from the BPS. The splicing factor U2AF, which is composed of two subunits (U2AF 65 and U2AF 35 ), binds to the pyrimidine tract in the E complex, with U2AF 65 directly contacting the pre-mRNA (4, 33 [for reviews, see references 17, 25, and 32]). The essential splicing factor SF1 (also known as mBBP) interacts with U2AF 65 and also has sequence specificity for the BPS (2, 5, 16). Thus, this network of interactions is thought to function in the initial recognition of the pyrimidine tract and BPS.The BPS is recognized a second time during spliceosome assembly by formation of a duplex between the BPS and U2 snRNA (for review, see reference 19). This duplex is first established in the A complex and plays an essential role in splicing by specifying the branch-site adenosine as the nucleophile for catalytic step I (23). Two multisubunit splicin...

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Formidable challenges for Parkinson's disease (PD) research are to understand the processes underlying nigrostriatal degeneration and how to protect the dopamine neurons. Fundamental research relies on good animal models that demonstrate the pathological hallmarks and motor deficits of PD. Using a chronic regimen of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and probenecid (MPTP/p) in mice, dopamine cell loss exceeds 60%, extracellular glutamate is elevated, cytoplasmic inclusions are formed and inflammation is chronic. Nevertheless, isradipine, an L-type calciumchannel blocker, attenuates the degeneration. These data support the validity of the MPTP/p model for unravelling the degenerative processes in PD and testing therapies that slow their progress.

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