1. EMBL/CRG Systems Biology Research Unit, Centre for Genomic Regulation (CRG), UPF, 08003 Barcelona, Spain
2. EMBL, Meyerhofstrasse 1, Heidelberg D-69117, Germany

Correspondence to: Mark Isalan¹ Correspondence and requests for materials should be addressed to M.I. (Email: isalan@crg.es).

Abstract

Sequencing DNA from several organisms has revealed that duplication and drift of existing genes have primarily moulded the contents of a given genome. Though the effect of knocking out or overexpressing a particular gene has been studied in many organisms, no study has systematically explored the effect of adding new links in a biological network. To explore network evolvability, we constructed 598 recombinations of promoters (including regulatory regions) with different transcription or -factor genes in Escherichia coli, added over a wild-type genetic background. Here we show that 95% of new networks are tolerated by the bacteria, that very few alter growth, and that expression level correlates with factor position in the wild-type network hierarchy. Most importantly, we find that certain networks consistently survive over the wild type under various selection pressures. Therefore new links in the network are rarely a barrier for evolution and can even confer a fitness advantage.

1. EMBL/CRG Systems Biology Research Unit, Centre for Genomic Regulation (CRG), UPF, 08003 Barcelona, Spain
2. EMBL, Meyerhofstrasse 1, Heidelberg D-69117, Germany

Correspondence to: Mark Isalan¹ Correspondence and requests for materials should be addressed to M.I. (Email: isalan@crg.es).