The protein content of a cell at any particular time and under specific conditions constitutes its proteome. The analysis of the entire cell's proteome or that of a subcellular structure or organelle has the potential to allow us to solve important biological questions.

This is illustrated by two recent research papers that are highlighted this month. As discussed in "A good place to start" (page 512), scientists analysed the proteome of the mammalian midbody in the hope of identifying new cytokinesis proteins. This analysis revealed a wealth of unknown proteins that can now be further characterized. It also provided insights into the mechanisms of cytokinesis. The second paper (highlighted in "Spread the word" on page 510) describes the identification of proteins that interact with focal-adhesion proteins during cell spreading. The researchers found, rather surprisingly, that certain RNA-binding proteins and RNA function during this process.

Proteomic studies of mitochondria have already uncovered a large number of unknown proteins. These approaches will prove invaluable in determining the composition of protein complexes, such as the mitochondrial translocation machines. This is discussed by Peter Rehling, Katrin Brandner and Nikolaus Pfanner on page 519 – they argue that for a full mechanistic understanding of the complex processes of mitochondrial protein transport, it is essential to know the complete set of players.

Taking proteomic analysis one step further, the development of oligosaccharide microarrays would allow us to define carbohydrate-recognition systems on a whole-organism scale. On page 582, Ten Feizi and Wengang Chai describe neoglycolipid technology. It entails the generation of oligosaccharide probes with lipid tags from desired biological sources – that is, from the complete sets of carbohydrates of cells, tissues and organisms.