Membrane traffic between genomes

Much has been said and written about the impact of the availability of complete genome sequences on biology. Rather less emphasis has been placed on the potential use of comparing genomes, particularly eukaryotic ones - not only to illuminate the evolutionary relations between organisms, but also to understand the organization of basic biological processes. Genomic information alone can allow the formulation, and even testing, of quite specific hypotheses. When the genomes are from organisms that are readily amenable to experiments, the potential to test such hypotheses is obviously much greater. At the time of writing, the protein-coding parts of four genomes of experimentally amenable eukaryotes are substantially available: the budding yeast Saccharomyces cerevisiae, the nematode Caenorhabditis elegans, the fruitfly Drosophila melanogaster and, with rather less fanfare thus far, the fission yeast Schizosaccharomyces pombe [1]. Here, I offer a preliminary glimpse at how these four genomes can influence our view of the cellular processes of membrane trafficking.Eukaryotic cells comprise a collection of discrete membrane-enclosed organelles with different functions, and hence distinct complements of proteins. Given that nearly all of these proteins are made by the same translation apparatus, the cell requires mechanisms to send different proteins to, and between, different organelles. Movement between organelles occurs by means of vesicles: patches of membrane that pinch off one organelle, taking a selected group of its proteins, and fuse with another. To preserve the identity of the organelles, each vesicle must know its destination. The members of two different protein families, the Rabs and the SNAREs, have been implicated in targeting different vesicles to distinct organelles. How large are these families in different eukaryotes? And can the differences between the complements of Rabs and SNAREs be correlated to differences in intracellular organization, and soph