Structural studies on colicin E3 and its immunity protein
Colicin E3 is a bacteriocin that penetrates sensitive cells and kills them by an enzymatic mode of action. It acts as a highly specific RNase that cleaves 16S ribosomal RNA at a position 49 bases in from the 3’end (Nomura et al. 1974). Although only a single phosphodiester bond is cleaved and the fragments stay attached to each other following the endonucleolytic attack, protein biosynthesis ceases completely and the infected cell dies. Colicin E3 acts in this specific manner only if all the components necessary for ribosome function are present. Thus, colicin E3 function requires the presence of the 50S subunit in addition to the 30S subunit as well as ribosomal proteins (Jakes & Zinder, 1974; Sidikaro & Nomura, 1974). Knowledge of the three-dimensional structure of colicin E3 will therefore not only provide an understanding of its mode of action but it is expected also to shed light on the structure of the ribosome at large in the vicinity of the cutting site. This region of the ribosome close to the interface between the small and large subunit is obviously critical for protein biosynthesis if a single nick in 16S RNA totally inactivates the ribosome.
KeywordsCrystallization Migration HPLC Mercury Citrate
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