Acid-loving bacterium reads its DNA with enzyme strikingly similar to yours
Transcription, the process of converting DNA into RNA (which in turn is translated into proteins by ribosomes) is carried out by the multisubunit RNA polymerase (RNAP) enzyme. Transcription is fundamental to all organisms across the three kingdoms of life – Eukarya, Bacteria, and Archaea – and can be divided into three major steps: initiation, transcription/elongation, and termination. Eukaryotes have three different nuclear RNAPs, whereas Archaea and Bacteria have one. Archaeal transcription is similar to that of eukaryotes, but initiation requires only two accessory proteins bound to DNA: transcription factor B (TFB) and TATA-box binding protein (TBP). It is believed that studies of the archaeal enzyme may shed light on the more complex eukaryotic RNAP. New research has shown that organisms which live in boiling acid read their DNA using enzymes surprisingly similar to our own, providing insight into the way in which the information stored in DNA is unlocked. This new work has shown that the enzyme that converts DNA into RNA is conserved between simple single-celled microorganism Sulfolobus and more complicated “higher” organisms, including human beings, despite a staggering 2 billion year evolutionary gulf. A new paper explores how evolution has shaped our own RNAP enzyme to accomplish more complex functions.
Many Archaea are extremophiles; living in high salt, acid or temperature environments. Transcription, the process of reading DNA to make RNA (which is in turn translated into proteins by ribosomes) is a fundamental process common to all organisms, and is carried out by the enzyme multisubunit RNA polymerase (RNAP). Eukaryotes have three different RNAPs, whereas Archaea and Bacteria have one. Archaea can serve as a wonderful model system because their simpler RNA polymerase machinery is related to the more complex eukaryotic RNAP. To start transcription, the archaeal enzyme requires two accessory proteins whilst the eukaryotic counterpart needs at least two more. This increased complexity prompts two important questions: how did our polymerase evolve from the ancestral enzyme; and how does Archaea bypass the requirement of further co-factor proteins?
New work investigates the polymerase from the Archaeon Sulfolobus shibatae using X-ray crystallography. This reveals the enzyme’s architecture which confirms its close evolutionary relationship with the eukaryotic RNAP. The research also identified a subunit novel to Sulfolobus which has no equivalent in the eukaryotic enzyme. The striking structural similarities suggest that the ancestral eukaryote used the same enzyme as the Archaeon, and that modern eukaryotic RNAP evolved by the addition of bolt-on proteins that regulate eukaryotic-specific processes. From the location and topology of the newly identified, Archaeon-only subunit, the scientists have suggested a mechanism by which Archaea do without the additional cofactors required by eukaryotes for initiating transcription. The scientists also noted that the complete structure of the archaeal polymerase illustrates how the ancestral core enzyme was modulated by addition of novel subunits, an evolutionary process that has facilitated the complexity that we see today in Eukarya.
Evolution of complex RNA polymerases: The complete archaeal RNA polymerase structure. 2009 PLoS Biol 7(5): e1000102
The archaeal RNA polymerase (RNAP) shares structural similarities with eukaryotic RNAP II but requires a reduced subset of general transcription factors for promoter-dependent initiation. To deepen our knowledge of cellular transcription, we have determined the structure of the 13-subunit DNA-directed RNAP from Sulfolobus shibatae at 3.35 A° resolution. The structure contains the full complement of subunits, including RpoG/Rpb8 and the equivalent of the clamp-head and jaw domains of the eukaryotic Rpb1. Furthermore, we have identified subunit Rpo13, an RNAP component in the order Sulfolobales, which contains a helix-turn-helix motif that interacts with the RpoH/Rpb5 and RpoA9/Rpb1 subunits. Its location and topology suggest a role in the formation of the transcription bubble.
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Tags: Bacteria, Biology, DNA, enzyme, Microbiology, Science, Sulfolobus
