1. Cell Cycle Laboratory, Imperial Cancer Research Fund, 44 Lincoln's Inn Field, London WC2A 3PX, UK
2. Present address: Department of Biophysics and Biochemistry, Graduate School of Science, University of Tokyo, Hongo, Tokyo 113, Japan.

Correspondence to: Yoshinori Watanabe¹ Correspondence and requests for materials should be addressed to Y.W. (e-mail: Email: ywatanab@ims.u-tokyo.ac.jp).The GenBank accession number of rec8 cDNA sequence is ABO 18077.

Abstract

When cells exit from mitotic cell division, their sister chromatids lose cohesion and separate to opposite poles of the dividing cell, resulting in equational chromosome segregation. In contrast, the reductional segregation of the first stage of meiotic cell division (meiosis I) requires that sister chromatids remain associated through their centromeres and move together to the same pole. Centromeric cohesion is lost as cells exit from meiosis II and sister chromatids can then separate¹,²,³,⁴. The fission yeast cohesin protein Rec8 is specific to and required for meiosis⁵,⁶,⁷,⁸. Here we show that Rec8 appears in the centromeres and adjacent chromosome arms during the pre-meiotic S phase. Centromeric Rec8 persists throughout meiosis I and disappears at anaphase of meiosis II. When the rec8 gene is deleted, sister chromatids separate at meiosis I, resulting in equational rather than reductional chromosome segregation. We propose that the persistence of Rec8 at centromeres during meiosis I maintains sister-chromatid cohesion, and that its presence in the centromere-adjacent regions orients the kinetochores so that sister chromatids move to the same pole. This results in the reductional pattern of chromosome segregation necessary to reduce a diploid zygote to haploid gametes.