The Life-Cycle of Operons
The Life-Cycle of Operons Morgan N. Price1,2, Adam P. Arkin1,2,3,4, Eric J. Alm1,2¤* 1 Lawrence Berkeley National Laboratory, Berkeley, California, United States of America, 2 Virtual Institute for Microbial Stress and Survival, University of California San Francisco, San Francisco, California, United States of America, 3 Department of Bioengineering, University of California Berkeley, Berkeley, California, United States of America, 4 Howard Hughes Medical Institute, University of California Berkeley, Berkeley, California, United States of America Operons are a major feature of all prokaryotic genomes, but how and why operon structures vary is not well understood. To elucidate the life-cycle of operons, we compared gene order between Escherichia coli K12 and its relatives and identified the recently formed and destroyed operons in E. coli. This allowed us to determine how operons form, how they become closely spaced, and how they die. Our findings suggest that operon evolution may be driven by selection on gene expression patterns. First, both operon creation and operon destruction lead to large changes in gene expression patterns. For example, the removal of lysA and ruvA from ancestral operons that contained essential genes allowed their expression to respond to lysine levels and DNA damage, respectively. Second, some operons have undergone accelerated evolution, with multiple new genes being added during a brief period. Third, although genes within operons are usually closely spaced because of a neutral bias toward deletion and because of selection against large overlaps, genes in highly expressed operons tend to be widely spaced because of regulatory fine-tuning by intervening sequences.
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