MCM21 and MCM22, two novel genes of the yeast Saccharomyces cerevisiae are required for chromosome transmission

Abstract

SummaryThe minichromosome maintenance genes, MCM21 and MCM22, have been cloned and are shown to code for the ORFs YDR318W and YJR135C respectively. Mutations in these genes caused a decrease in the stability of the minichromosome. This decrease in stability was associated with an increase in the copy number of the minichromosome in cells carrying it. Small circular dicentric plasmids were maintained relatively stably and structurally intact in the mutants compared with the wild-type strain. In the latter, such plasmids were mitotically unstable and, upon recovery, showed frequent rearrangements of their DNA. A centromere offered less obstruction to transcription in mutant cells than in the wild type, showing that both these mutants had a more relaxed kinetochore assembly. The mutant strains showed elevated rates of chromosome loss but not those of recombination. Both the mutations caused the cells to display a higher sensitivity towards the anti-mitotic drug benomyl. All these observations suggest that MCM21 and MCM22 are important for chromosome segregation with a potential role in kinetochore function. These genes are nonessential, as their deletions from chromosomes did not cause loss of cell viability. However, exponentially growing mutant cells carrying the deletion of the MCM21 gene had a significant population of largebudded cells with a single nucleus at the neck. Furthermore, the DNA content of these cells showed a shift towards 2N, suggesting a temporary pause of cells in G 2 or in an early phase of mitosis. The mcm21 and mcm22 mutations do not show synthetic lethality or any further enhancement of growth defects, implying that they could be carrying out non-overlapping functions in chromosome segregation.

The Composition, Functions, and Regulation of the Budding Yeast Kinetochore

“…COMA and interacting proteins Additional components of the yeast inner kinetochore include the COMA subcomplex (Ctf19, Okp1, Mcm21 and Ame1), as well as many additional interacting proteins (see Table 1) (Kroll et al 1996;Sanyal et al 1998;Hyland et al 1999;Ortiz et al 1999;Poddar et al 1999;Cheeseman et al 2002;Measday et al 2002;De Wulf et al 2003;Pot et al 2003;Ohkuni et al 2008;Schleiffer et al 2012). With the exception of Okp1 and Ame1, most of these proteins are nonessential and may have redundant functions.…”

Ctf3p, the Mis6 budding yeast homolog, interacts with Mcm22p and Mcm16p at the yeast outer kinetochore

“…Mcm22p was identified in two independent screens as a Ctf3p interacting protein. mcm22 mutant strains lose chromosome III 100-fold more frequently than wild-type strains and have other phenotypes implicating a role for Mcm22p at the kinetochore (Maine et al 1984;Poddar et al 1999). Interestingly, genome-wide two-hybrid screens identified Mcm16p and Mcm22p as interacting partners (Uetz et al 2000).…”

“…Secondary screens applied to the ctf mutant collection successfully identified Ctf13p, Ndc10p/Ctf14p, and Ctf19p as kinetochore proteins (Doheny et al 1993;Kroll et al 1996;Hyland et al 1999). In addition to a high rate of chromosome loss, a subset of mcm, chl, and ctf mutants display phenotypes reminiscent of kinetochore mutants (Doheny et al 1993;Kouprina et al 1993;Roy et al 1997;Sanyal et al 1998;Poddar et al 1999;Ghosh et al 2001). Thus new kinetochore proteins remain to be identified from these chromosome loss mutant collections.…”

Mitch – a rapidly evolving component of the Ndc80 kinetochore complex required for correct chromosome segregation inDrosophila

“…Mutations that disrupted the fidelity of chromosome segregation led to the discovery of kinetochore proteins, such as Ctf19, Mcm21 and Cin8 (Hoyt et al, 1992;Poddar et al, 1999;Spencer et al, 1990). Most of the canonical SAC proteins were originally identified through screens for mutations that prevented cells from arresting mitosis in the presence of spindle poisons (Hoyt et al, 1991;Li and Murray, 1991).…”