ON THE TIME OF REFLEX WINKING

I. The mean total time taken from 450 experiments on sixteen subjects was found to be 0.0420 second. II. Natural winks occurring very shortly before the record was taken had no influence. III. The reflex time was found to vary in different individuals, the limits of the mean times being 0.0351 and 0.0491 second. For any given individual there was a close correspondence between averages of sets of experiments obtained under similar conditions. In the case of one man this was true of sets of experiments taken a year apart. Sex has no influence. IV. Apprehension seems to shorten the time

Transcription factor regulation and chromosome dynamics during pseudohyphal growth

Pseudohyphal growth is a developmental pathway seen in some strains of yeast in which cells form multicellular filaments in response to environmental stresses. We used multiplexed transposon “Calling Cards” to record the genome-wide binding patterns of 28 transcription factors (TFs) in nitrogen-starved yeast. We identified TF targets relevant for pseudohyphal growth, producing a detailed map of its regulatory network. Using tools from graph theory, we identified 14 TFs that lie at the center of this network, including Flo8, Mss11, and Mfg1, which bind as a complex. Surprisingly, the DNA-binding preferences for these key TFs were unknown. Using Calling Card data, we predicted the in vivo DNA-binding motif for the Flo8-Mss11-Mfg1 complex and validated it using a reporter assay. We found that this complex binds several important targets, including FLO11, at both their promoter and termination sequences. We demonstrated that this binding pattern is the result of DNA looping, which regulates the transcription of these targets and is stabilized by an interaction with the nuclear pore complex. This looping provides yeast cells with a transcriptional memory, enabling them more rapidly to execute the filamentous growth program when nitrogen starved if they had been previously exposed to this condition