The HFD of Cse4p is sufficient for a functional centromere specific nucleosome: An investigation into kinetochore formation on <i>cen</i> DNA
Centromeres are the site on a chromosome that allows for proper chromosome segregation during cell division. The kinetochore, a DNA-protein complex that forms at the centromere, attaches the chromosome to the spindle fiber and therefore ensures faithful separation of the chromosomes. Cse4p was identified in the budding yeast S. cerevisiae and is protein that resembles histone H3. Due to its centromere specific localization led to the proposal of the centromere specific nucleosome(s). Further identification of Cse4p homologues in many diverse organisms, including mammalian systems, supported the idea that the centromere specific nucleosome is an evolutionarily conserved structure.
The localization of the centromere specific histone H3-like proteins (CenH3) to the centromere is one of the remaining questions in centromere biology. It is known that the CenH3 proteins have two domains, the conserved Histone Fold Domain (HFD), and a unique N-terminus, and that each domain has a distinct function. I analyzed the function of the Cse4 N-terminus and HFD in centromere localization and showed that the N-terminus has no function in centromere localization, but rather is involved in regulating Cse4 protein turnover. The HFD, therefore, contains all the centromere targeting information and is necessary and sufficient for Cse4 function. Further analysis revealed that the specific DNA contacts of the Cse4 HFD are important for localization to the centromere.
In the budding yeast, S. cerevisiae, the centromere DNA is defined by a specific DNA sequence that is divided into three distinct regions, CDEI, II, and III. Mutations of these regions affect centromere function to varying degrees. Analysis of Cse4p localization to mutant centromere constructs revealed that CDEII is necessary for Cse4 centromere localization, but that the intrinsic bend of this element is not involved in Cse4p centromere localization. Cse4p localization to two other centromere mutants, cen3-X35 and cen3-X50, was analyzed. Cse4p could recognize cen3-X35, a construct with a CDEII deletion, but failed to recognize cen3-X50, a CDEII and CDEIII mutant centromere construct. Furthermore, the CBF3 complex was present at both of these centromere constructs, indicating that the CDEIII by deleted in cen3-X50 directly affects Cse4p centromere localization.
0379: Cellular biology