Cellular signaling can be complex and dynamic. In the past several decades, it has become clear that many signal transduction pathways are not simple one-way transmissions of upstream stimuli, but are mediated through extremely complicated networks. Our next challenge is to move beyond the static biochemical description of networks into developing a functional quantitative understanding of their behavior. In this Minisymposium, we presented diverse approaches for beginning to achieve this goal. Galit Lahav (Harvard Medical School) opened the session and demonstrated how the temporal dynamics of the tumor suppressor protein p53 in single cells affect cell fate decisions. Cells that naturally show a series of p53 pulses in response to irradiation and recover from the damage were perturbed to instead show sustained p53. This perturbation led to activation of different target genes and pushed cells toward permanent cell cycle arrest. p53 dynamics therefore contribute to transferring information in cells and provide a new axis for pushing cells toward a specific cellular outcome. Andrei V. Karginov (University of Illinois at Chicago) focused on the spatiotemporal regulation of the Src signaling pathway by engineering a chimera of the Src kinase domain and an insertable FKBP12 protein, iFKBP. By fusing the FKBP12-rapamycin binding domain (FRB) to the specific downstream effectors, he restricted the Src activation to the complex it forms with FRB-bearing downstream targets. He presented evidence that a specific complex of Src and FAK leads to focal adhesion, while a complex of Src and p130Cas leads to filopodia formation. Robin E. Lee (Dana-Farber Cancer Institute) demonstrated that, upon tumor necrosis factor-α (TNF-α) stimulation, the early-response genes of NF-κB use memory to assess NF-κB activation. He analyzed the nuclear translocation dynamics of p65, a major NF-κB transcription factor, and then the number of mRNA transcripts for target genes in the same cells. The gene transcriptions of three early-response genes, IL8, A20, and IκB α, were regulated by the fold changes of nuclear NF-κB. His results, supported by computational modeling, suggest that competitive transcription factor–DNA interactions can provide memory of pre-ligand NF-κB states, allowing fold-change signal detection. The NF-κB signaling pathway has been also shown to involve ubiquitin modification of important molecules. Fumiyo Ikeda (Institute of Molecular Biotechnology) reported that an atypical type of ubiquitin chain, linearly linked chains, plays a critical role in the regulation of a Sharpin-dependent, anti-apoptotic pathway downstream of TNF. She presented a critical apoptosis signaling molecule, FADD, as a novel substrate of the Sharpin-containing E3 ligase that plays a role in the regulation of the apoptotic cascade. Jeffery A. Nickerson (University of Massachusetts Medical School) focused on the regulation of mRNA export by phosphatidylinositol 3-kinase/protein kinase B (PI3 kinase/Akt) signal transduction. His group implemented a fluorescence recovery after photobleaching system for screening signal transduction pathways that regulate mRNA nuclear export and the binding of the exon junction complex core proteins. By combining the analysis of mRNA export to the cytoplasm, they showed that the PI3 kinase/AKT pathway regulates not only mRNA export complex formation, but also the rate of mRNA nuclear export. Anna Podgornaia (Massachusetts Institute of Technology) tackled a challenging question to understand the transient protein–protein interaction surface that determines protein pairing by using a systematic mutagenesis approach. She focused on the histidine kinase PhoQ and its cognate response regulator PhoP, which together regulate bacterial signaling. Out of 160,000 PhoQ variants completely randomized at four residues, 4600 variants were signal-responsive. She is exploring why all these 4600 sequences are not used by extant PhoQ orthologues, which only have 260 different interface sequences.