Counting the Core
S. Ohta et al., "The protein composition of mitotic chromosomes determined using multiclassifier combinatorial proteomics," Cell, 142:810-21, 2010. Free F1000 Evaluation
Despite the central importance of chromosomes, very little is understood about the more than 120 proteins present at the kinetochore, the complex of proteins involved in connecting the spindle fibers to the centromere during mitosis—not even how many are functionally relevant. Using a clever combination of genetic, proteomic, and computational techniques, Bill Earnshaw and colleagues at the University of Edinburgh identified which proteins should be studied, and proposed that almost 100 more kinetochore proteins remain to be characterized.
Using mass spectroscopy, Earnshaw's team measured the protein content of kinetochores at different stages of the cell cycle and compared the protein profiles to those of cells that lack some chromosomal proteins.
Because mass-spec experiments can miss relevant proteins, the researchers created six data classifiers for their chromosome comparisons. The classifiers could fill in missed proteins and determine the likelihood of a protein's functional relevance.
This “powerful resource,” writes Faculty Member Iain Cheeseman, can be used as a first step in studying other structures that don’t have well-defined boundaries and are therefore difficult to purify, such as neuromuscular junctions or centrosomes. Earnshaw plans to use the method to help build a complete molecular model of the entire kinetochore.