In 2005 he moved to the recently created Department of Systems Biology at Harvard University, where he focused on the development of experimental techniques for counting plasmids in single cells and on theoretical results on control of fluctuations in gene expression.
A publication is the analysis of all previous noise data and interpretations in one unified framework,[12][13] which later guided many experimental approaches.
[14][15][16] More recent results include the effects of partition in phenotypic variability,[17] the details of the stochastic processes that underlie gene expression noise and the limitations of the usual experimental approaches[18][19] and the fundamental limits of feedback as a noise control mechanism.
[20] This set of interests led Paulsson to examine the repressilator, a synthetic gene regulatory network that was designed from scratch to oscillate and reported in 2000[21] by Michael Elowitz and Stanislas Leibler.
Using an understanding of the causes of noise in cellular networks, Paulsson's team was able to redesign the repressilator, retaining the basic design, to produce a new synthetic circuit that oscillated with some accuracy.