The protein content of a cell is a primary determinant of its phenotype. Yet, large fluctuations in protein numbers are observed among genetically identical cells grown under identical conditions. Recently, cellular protein variability has been a hot topic of research, with microorganisms providing a popular model system. Despite much work and much progress in the field, a general integrative picture is still lacking. This seminar will report recent experimental results obtained in collaboration with the groups of H. Salma, E. Braun and A. Libchaber, and their theoretical implications. We have shown that protein distributions measured under a broad range of biological realizations collapse to a single non-Gaussian curve under scaling by the first two moments. Moreover in all experiments the variance is found to depend quadratically on the mean, showing that a single degree of freedom determines the entire distribution. Our results imply that protein fluctuations do not reflect any specific molecular or cellular mechanism, and suggest that some buffering process masks these details and induces universality. Non-Gaussian universal distributions with qualitatively similar features to those we measured were observed in various complex physical systems at or near criticality. This analogy calls for an understanding of cell populations in a broader context with an emphasis on many-body interactions and long range correlations.
Lunch @ 11:45, talk @ 12-1:00