Focus issue: regulation of lymphocyte function.

During the month of July, Science Signaling has highlighted mechanisms by which lymphocytes of the innate and adaptive immune responses are regulated to promote effective immunity and prevent inappropriate and damaging responses. Research Articles and Perspectives in this series and the Archives focus on the mechanisms by which the functions of T cells, B cells, and natural killer cells are regulated and the therapeutic implications of understanding the regulation of these cells.

Mechanism of actin filament turnover by severing and nucleation at different concentrations of ADF/cofilin.

ADF/cofilins are key regulators of actin dynamics during cellular motility, yet their precise role and mechanism of action are shrouded in ambiguity. Direct observation of actin filaments by evanescent wave microscopy showed that cofilins from fission yeast and human do not increase the rate that pointed ends of actin filaments shorten beyond the rate for ADP-actin subunits, but both cofilins inhibit elongation and subunit dissociation at barbed ends. Direct observation also showed that cofilins from fission yeast, Acanthamoeba, and human sever actin filaments optimally at low-cofilin binding densities well below their K(d)s, but not at high binding densities.

Synthetic biology: new engineering rules for an emerging discipline.

Synthetic biologists engineer complex artificial biological systems to investigate natural biological phenomena and for a variety of applications. We outline the basic features of synthetic biology as a new engineering discipline, covering examples from the latest literature and reflecting on the features that make it unique among all other existing engineering fields. We discuss methods for designing and constructing engineered cells with novel functions in a framework of an abstract hierarchy of biological devices, modules, cells, and multicellular systems.