Starch consumption is a prominent characteristic of agricultural societies and hunter-gatherers in arid environments. In contrast, rainforest and circum-arctic hunter-gatherers and some pastoralists consume much less starch 1-3 . This behavioral variation raises the possibility that different selective pressures have acted on amylase, the enzyme responsible for starch hydrolysis 4 . We found that salivary amylase gene (AMY1) copy number is correlated positively with salivary amylase protein levels, and that individuals from populations with high-starch diets have on average more AMY1 copies than those with traditionally low-starch diets. Comparisons with other loci in a subset of these populations suggest that the level of AMY1 copy number differentiation is unusual. This example of positive selection on a copy number variable gene is one of the first in the human genome. Higher AMY1 copy numbers and protein levels likely improve the digestion of starchy foods, and may buffer against the fitness-reducing effects of intestinal disease. Hominin evolution is characterized by significant dietary shifts, facilitated in part by the development of stone tool technology, the control of fire, and most recently the domestication of plants and animals 5-7 . Starch, for instance, has become an increasingly prominent component of the human diet, particularly among agricultural societies 8 . It stands to reason, therefore, that studies of the evolution of amylase in humans and our close primate relatives may provide insight into our ecological history. Because the human salivary amylase gene (AMY1) shows extensive variation in copy number 9,10 , we first assess whether a functional relationship exists between AMY1 copy number and the level of amylase protein expression in

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Filament-forming cytoskeletal proteins are key organizers of all cells. Bacterial homologs of the major eukaryotic cytoskeletal families have now been discovered, but studies suggest that yet more cytoskeletal proteins remain to be identified. Here we demonstrate that the metabolic enzyme CTP Synthase (CtpS) forms filaments in Caulobacter crescentus. These filaments are bifunctional and regulate Caulobacter curvature independently of CtpS catalytic activity. The morphogenic role of CtpS requires its functional interaction with the intermediate filament crescentin. Interestingly, the E. coli CtpS homolog also forms filaments both in vivo and in vitro, suggesting that CtpS polymerization may be widely conserved. E. coli CtpS can replace the enzymatic and morphogenic functions of Caulobacter CtpS, indicating that Caulobacter has adapted a conserved filament-forming protein for a secondary role. These results implicate CtpS as a novel bifunctional member of the bacterial cytoskeleton and suggest that localization and polymerization may be important properties of metabolic enzymes.

Despite the importance of subcellular localization for cellular activities, the lack of high-throughput, high-resolution imaging and quantitation methodologies has limited genomic localization analysis to a small number of archival studies focused on Cterminal fluorescent protein fusions. Here, we develop a highthroughput pipeline for generating, imaging, and quantitating fluorescent protein fusions that we use for the quantitative genomic assessment of the distributions of both N-and C-terminal fluorescent protein fusions. We identify nearly 300 localized Caulobacter crescentus proteins, up to 10-fold more than were previously characterized. The localized proteins tend to be involved in spatially or temporally dynamic processes and proteins that function together and often localize together as well. The distributions of the localized proteins were quantitated by using our recently described projected system of internal coordinates from interpolated contours (PSICIC) image analysis toolkit, leading to the identification of cellular regions that are over-or under-enriched in localized proteins and of potential differences in the mechanisms that target proteins to different subcellular destinations. The Caulobacter localizome data thus represent a resource for studying both global properties of protein localization and specific protein functions, whereas the localization analysis pipeline is a methodological resource that can be readily applied to other systems.bacteria ͉ Caulobacter ͉ genomics ͉ quantitative image analysis ͉ high-throughput imaging T he emergence of high-throughput methods to assay the levels of cellular components such as mRNAs and proteins has enabled the study of biological processes at a systems level, enhancing the understanding of both individual proteins and functional modules. Meanwhile, the subcellular localizations of proteins that mediate such cellular processes as growth, division, and motility indicate that many important aspects of cell biology require precise spatial organization. The significance of this localization holds true in both eukaryotes and prokaryotes. Large-scale efforts have cataloged the localizations of Cterminal GFP fusions to most of the proteins of Saccharomyces cerevisiae, Schizosaccharomyces pombe, and Escherichia coli (1-3). However, the utility of these libraries has been limited by the laborious nature of generating, imaging, and scoring fluorescent fusions, thereby restricting their reanalysis under different conditions and reconstruction as N-terminal fusions or fusions to other fluorescent proteins. Furthermore, protein localization has classically been analyzed via qualitative descriptors that limit their utility for quantitative systems-level characterizations.Despite their small size and lack of internal compartmentalization, bacterial cells are highly organized (4). Relatively small genomes and experimental tractability thus make bacteria powerful systems for studying universal cell biological processes such as cell division, cell cycle progression, a...

SUMMARY FtsZ is an essential bacterial GTPase that polymerizes at midcell, recruits the division machinery, and may generate constrictive forces necessary for cytokinesis. However, many of the mechanistic details underlying these functions are unknown. We sought to identify FtsZ-binding proteins that influence FtsZ function in Caulobacter crescentus. Here, we present a microscopy-based screen through which we discovered two FtsZ-binding proteins, FzlA and FzlC. FzlA is conserved in α-proteobacteria and was found to be functionally critical for cell division in Caulobacter. FzlA altered FtsZ structure both in vivo and in vitro, forming stable higher order structures that were resistant to depolymerization by MipZ, a spatial determinant of FtsZ assembly. Electron microscopy revealed that FzlA organizes FtsZ protofilaments into striking helical bundles. The degree of curvature induced by FzlA depended on the nucleotide bound to FtsZ. Induction of FtsZ curvature by FzlA carries implications for regulating FtsZ function by modulating its superstructure.