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Abstract
Ribosome recycling factor (RRF), coded for by the frr locus, is involved in the disassembly of post-termination complexes and recycling of the ribosomes for a fresh round of initiation in bacteria and in eukaryotic organelles. In a cross-species-complementation experiment, it was shown that the Thermus thermophilus RRF protein lacking five amino acids from its C-terminal end (ΔC5TthRRF) but not the full-length protein (TthRRF) complemented Escherichia coli for its frr ts phenotype. It was also shown that the Mycobacterium tuberculosis RFF protein (MtuRRF) did not complement E. coli LJ14 for frr ts. However, simultaneous expression of elongation factor G (EFG) and RRF from M. tuberculosis resulted in complementation of E. coli LJ14. Here it is shown that unlike ΔC5TthRRF, an equivalent mutant of MtuRRF lacking six amino acids from its C-terminal end (ΔC6MtuRRF) did not complement E. coli LJ14. Surprisingly, ΔC6MtuRRF failed to complement the strain even in the presence of homologous EFG (MtuEFG). The biochemical and biophysical characterization of these proteins suggested that the mutant RRF folded properly. However, ribosome-binding assays showed that the mutant protein was compromised in its binding to E. coli ribosomes. It is suggested that the conserved amino acids at the C-terminal end of the RRFs contribute to their residency on ribosomes and that the specific interactions between RRF and EFG are crucial in the disassembly of the termination complex.
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