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Contrary to what’s typically described in biology textbooks, bacteria and archaea can have transcription proceed in opposite directions on the genome. This occurs thanks to bidirectional promoters—DNA sequences where RNA polymerases can hop on and travel one way or the other to produce mRNA transcripts. Such promoters aren’t rare occurrences: 19 percent of all transcription start sites (TSSs) in Escherichia coli are associated with a bidirectional promotor, according to a study published May 6 in Nature Microbiology.
“We were really surprised,” says study coauthor Emily Warman, a molecular microbiology postdoc at the University of Birmingham in the UK. While previous research had described bidirectional promoters in eukaryotes, as well as in a few bacteria and archaea species, the new study establishes divergent transcription—the reading of genes in both directions—as a widespread feature conserved across all three domains of life.
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