A group of researchers led jointly by the California Institute of Technology (Caltech), the University of Cambridge and Pompeu Fabra University, has discovered a new system whereby the components of cells, such as proteins, share resources when they are scarce. “The system is comparable to time share used by different families to enjoy a holiday apartment at different times of the year”, explains the researcher of the Department of Experimental and Health Sciences (DCEXS) at UPF,  Jordi Garcia-Ojalvo, one of the authors of the study.

Often, in cells, some components have to compete actively when they only have a limited amount of a resource, such as an enzyme. The different components may share the enzyme, each one using a fraction of it steadily. But now it has be seen that they can use the resources in turns, that is to say, a component monopolizes the enzyme for a period of time and then gives way to another different component.

In a study published in 2017, Garcia-Ojalvo, in collaboration with colleagues at the University of California San Diego,  discovered that populations of bacteria called biofilms alternate their feeding periods in order to reduce competition and avoid collapses in consumption when the amount of nutrients is limited. “Then, we found that cell populations shared resources, and now we show that this phenomenon also occurs within a cell, indicating that time share is a general strategy of living systems”, says the full professor of Systems Biology.

Through experiments using fluorescence video microscopy, the researchers analysed the behaviour of individual cells of the bacterium Bacillus subtilis in stress conditions in which these organisms only have a limited amount of energy.  Specifically, they studied proteins called sigma factors, that compete for the RNA polymerase enzyme, required to read the genetic information of the bacteria. A mathematical model has revealed that two of these factors are rarely activated at the same time and that some are negatively correlated, i.e., when one is expressed the other is not. This indicates that the different elements alternate the use of the RNA polymerase in time.

Because the molecular components are limiting in many other systems, this time share strategy could represent a far more general regulation system. “The results help us to better understand how living organisms work, and reveal an unexpected connection between biology, economics and engineering: methods that humans use to share resources were invented by evolution hundreds of millions of years ago”, concludes Garcia-Ojalvo.

Reference article:

Jin Park, Marta Dies, Yihan Lin, Sahand Hormoz, Stephanie E. Smith-Unna, Sofia Quinodoz, María Jesús Hernásndez-Jiménez, Jordi Garcia-Ojalvo, James C.W. Locke and Michael B. Elowitz. Molecular Time Sharing through Dynamic Pulsing in Single Cells. Cell Systems, February 2018