Public Science Insights: Did ancient bacterial mRNA genes have introns?

Posted Tue, Apr, 18,2017


Ancient bacterial mRNA genes quite possibly had introns, according to recent findings by Dr. Wang and colleagues.

All current bacterial mRNA genes have no intron (nucleotide base sequence interrupting the coding regions, exons, in a gene), though current bacterial tRNA and rRNA genes have introns. Thus, it is thought that ancient bacterial mRNA genes did not have introns either. However, many studies have suggested that ancient bacterial mRNA genes should also have introns, though without supportive evidence. Since no ancient bacterial genes are available today, Dr. Wang and colleagues turned to study bacterial genes that had been transferred into eukaryotic organisms which have kept the bacterial genes more or less as they were received. Their findings provide a piece of supportive evidence to intron existence in ancient bacterial mRNA genes.

How ancient bacteria may have had intron-containing genes that were passed on to eukaryotes
A eukaryote, the sea anemone, contains a 40-base long intron in a gene (1), which has a high degree of similarity to a sequence found in a very similar gene in bacteria today (2). Current bacteria contain a location in the GT-poor region of this gene that may have served as the starting point for an intron (3). The authors posit that when ancient bacteria transferred this gene to eukaryotes, this 40-base long sequence was recognized by molecular machinery in eukaryotic cells as an intron. Over time, the original GT-region in bacteria may have mutated, resulting in excision or removal of part of this hypothetical intron sequence, leaving behind bases which form part of this same gene in bacteria today (4).

Dr Yong Wang is author of the recently published paper Current Bacterial Gene Encoding Capsule Biosynthesis Protein CapI Contains Nucleotides Derived from Exonization, available for download now in Evolutionary Bioinformatics.

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