Two distinct pathways responsible for the loading of CENP-A to centromeres in the fission yeast cell cycle

Abstract

CENP-A is a centromere-specific histone H3 variant that is-essential for faithful chromosome segregation in all eukaryotes thus far investigated. We genetically identified two factors, Ams2 and Mis6, each of which is required for the correct centromere localization of SpCENP-A (Cnp1), the fission yeast homologue of CENP-A. Ams2 is a cell-cycle-regulated GATA factor that localizes on the nuclear chromatin, including on centromeres, during the S phase. Ams2 may be responsible for the replication-coupled loading of SpCENP-A by facilitating nucleosomal formation during the S phase. Consistently, overproduction of histone H4, but not that of H3, suppressed the defect of SpCENP-A localization in Ams2-deficient cells. We demonstrated the existence of at least two distinct phases for SpCENP-A loading during the cell cycle: the S phase and the late-G2 phase. Ectopically induced SpCENP-A was efficiently loaded onto the centromeres in G2-arrested cells, indicating that SpCENP-A probably undergoes replication-uncoupled loading after the completion of S phase. This G2 loading pathway of SpCENP-A may require Mis6, a constitutive centromere-binding protein that is also implicated in the Mad2-dependent spindle attachment checkpoint response. Here, we discuss the functional relationship between the flexible loading mechanism of CENP-A and the plasticity of centromere chromatin formation in fission yeast.

A high-resolution map of nucleosome positioning on a fission yeast centromere

“…www.genome.org acts with Cnp1p (Chen et al 2003a,b;Takahashi et al 2005;Takayama and Takahashi 2007). In either case, our work shows that the activity of Ams2 may influence the composition but not the locations of centromeric nucleosomes and thus argues against the nucleosome eviction hypothesis for functional centromeres (see Supplemental Fig.…”

“…Ams2p, a GATA-like transcription factor, has been shown to bind to the centromere core regions and plays an important role in localizing Cnp1p to centromeres during S phase (Chen et al 2003a,b;Takahashi et al 2005;Takayama and Takahashi 2007). The precise mechanism for how Ams2p facilitates Cnp1p loading is not known.…”

“…Importantly, the smeared pattern of cnt and imr is converted to the ladder pattern by mutations in Cnp1p and additional proteins that are functionally related to the kinetochore (Goshima et al 1999;Takahashi et al 2000Takahashi et al , 2005Hayashi et al 2004). These results indicate that in S. pombe a hitherto uncharacterized unique centromeric chromatin is intimately related to the functional kinetochore.…”

Chromosome segregation and organization are targets of 5′-Fluorouracil in eukaryotic cells

“…66 Mitotic cohesin is a multiprotein complex required for sister chromatid cohesion, spindle pole formation and chromosome movement in eukaryotes. 67 On the other hand, the NMS complex is necessary for the attachment of spindle microtubules to the kinetochore.…”

The role of the Mis18α-β complex and its interactions with HJURP and CENP-A in human centromeric chromatin establishment

“…Adding even more depth, fission yeast can deposit CENP-A/Cnp1 in both S and G2-phase 51,52 . CENP-A/CENH3 deposition in plants occurs during late G2-phase as well 53 .…”