The polyubiquitin gene is essential for meiosis in fission yeast

We isolated a novel sporulation-deficient mutant of Schizosaccharomyces pom be, The mutant did not have a mitotic growth defect but aborted meiosis at the first or the second division with condensed chromosomes that failed to separate, abnormal spindle(s), and disintegrated spindle pole bodies (SPBs) . During the first division, the centromeres were pulled to near the spindl e poles but condensed divalent chromosomes remained at the center. The fail ure to proceed to anaphase was also observed during a time-lapse recording of a SPB protein tagged with green fluorescent protein. The polyubiquitin g ene ubi4(+), which encoded eight ubiquitins fused in tandem, complemented t his mutant. The mutation, an A to G substitution, was identified within the ubi4+ gene at the ATG initiation codon. Disruption of the ubi4(+) gene pro duced the same phenotypes. The ubi4(+) mRNA was strongly induced for meiosi s. However, ubiquitin increases only slightly, suggesting that the role of the polyubiquitin gene is to supply ubiquitin that is consumed by unidentif ied mechanisms, Before the ubi4 mutant cells entered meiosis, ubiquitin was greatly decreased indicating that shortage of ubiquitin caused abortion of meiosis. This work provides insights for the role of polyubiquitin gene an d importance of ubiquitination in SPB integrity at the meiotic divisions. ( C) 2000 Academic Press.