The Schizosaccharomyces pombe spo6+ gene encoding a nuclear protein with sequence similarity to budding yeast Dbf4 is required for meiotic second division and sporulation.
BACKGROUND
Sporulation of the fission yeast Schizosaccharomyces pombe is a cell differentiation process which accompanies meiosis. The spo6+ gene was identified as a sporulation-specific gene, whose transcription was regulated by the forkhead family transcription factor Mei4.


RESULTS
spo6+ encodes a protein with sequence similarity to Saccharomyces cerevisiae Dbf4p, which is required for the initiation of DNA replication. However, doubling time and cell morphology of spo6 deletion mutants and spo6-cDNA over-expressing cells were indistinguishable from wild-type cells. Spliced mature mRNAs of spo6+ appeared when diploid cells committed to meiosis. Spo6p fused to green fluorescent protein (GFP) preferentially localized in a nucleus. Although spo6Delta diploids normally underwent premeiotic DNA replication and meiosis-I, approximately 80% of cells were blocked at the binucleate stage during meiosis and virtually no asci were formed. Anti-tubulin staining revealed that only 25% of the binucleate cells assembled spindle microtubules for meiosis-II. In a small number of tetranucleate cells, sister nuclei insufficiently separated and spindles were frequently fragmented. The meiosis-II arrest phenotype was exaggerated at low temperature and in the presence of caffeine.


CONCLUSIONS
These results indicate that Spo6p is a novel Dbf4-related nuclear protein, which is expressed during meiosis and is indispensable for normal progression of meiosis-II and sporulation.
Nakamura
T
T
Department of Biology, Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585, Japan.
Kishida
M
M
Shimoda
C
C
D020816:Amino Acid Motifs; D002110:Caffeine / Q000494:pharmacology; D018797:Cell Cycle Proteins; D002455:Cell Division / Q000187:drug effects / Q000235:genetics; D003001:Cloning, Molecular; D004271:DNA, Fungal / Q000096:biosynthesis; D004305:Dose-Response Relationship, Drug; D005656:Fungal Proteins / Q000235:genetics*; D015870:Gene Expression; D008540:Meiosis / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins / Q000235:genetics*; D012333:RNA, Messenger / Q000096:biosynthesis; D012441:Saccharomyces cerevisiae / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins; D012568:Schizosaccharomyces / Q000166:cytology* / Q000235:genetics* / Q000254:growth & development; D029702:Schizosaccharomyces pombe Proteins; D017386:Sequence Homology, Amino Acid; D013172:Spores, Fungal / Q000235:genetics / Q000254:growth & development
D018797:Cell Cycle Proteins; D004271:DNA, Fungal; C088096:Dbf4 protein, S cerevisiae; D005656:Fungal Proteins; D009687:Nuclear Proteins; D012333:RNA, Messenger; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins; C412765:Spo6 protein, S pombe; D002110:Caffeine