Editorial [Hot Topic: Yeast Systems Biology Special Issue (Guest Editor: Hiroaki Kitano)]

Yeast has been one of the most extensively investigated model organisms. It is the simplest eukaryote cell in which enormous variety of experimental techniques are readily available. This makes yeast ideal target for integrated study of cellular systems which is one of the salient feature of systems biology. In addition, there are continuous discoveries of significant new biology in yeast that are quickly identified also in mammalian species. Given the existence of sizable, coherent, collaborative, and passionate research community, it is expected that yeast will continue to provide us with new discoveries for integrated understanding of cellular systems. This special issue features several papers that discuss various aspects of budding yeast systems biology --- metabolisms, cell cycle, signal transductions, as well as large scale genome-wide measurements. These papers represent some of efforts that are now being made toward integrated system-level understanding of budding yeast. There are broad approaches and level to tackle the problem. Some papers describe genome-wide approaches whereas other papers describe more detailed modeling and experiments on specific aspects of cellular processes. Obviously, these approaches are complementary and expected to be integrated in future for a coherent view. A coordinated effort toward yeast systems biology is now beginning. The Yeast Systems Biology Network (YSBN: http: / / www.ysbn.org / ) has been established to network researchers interested in yeast systems biology, and to foster collaborations between researchers for ultimate goal of understanding the cell as a whole. While the effort is in its infancy, such efforts may leads to significant platform for the research community. It is unfortunate, however, that funding agencies are tends to underestimate the value of yeast as a model organism today. Given the cost and difficulties in manipulating and measuring mammalian cells, yeast is the most efficient and controllable eukaryote cell where system-wide investigation can be performed. Obviously, there are things that cannot be covered by yeast, such as development, neural systems, and immune systems, but I would expect that numbers of important discoveries on logic of cells will be made first in yeast, then followed by mammalian cells. I hope this issue help readers to get familiarize research on integrated understanding of yeast and to be inspirations to young researchers.