The N-end rule pathway is a conserved targeted proteolytic process observed in organisms ranging
from eubacteria to mammals. The N-end rule relates the metabolic stability of a protein to its N-terminal
amino acid residue. The identity of the N-terminal amino acid residue is a primary degradation signal, often
referred to as an N-degron, which is recognized by the components of the N-end rule when it is a destabilizing
N-terminus. N-degrons may be exposed by non-processive proteolytic cleavages or by post-translational
modifications. One modification is the post-translational addition of amino acids to the N-termini of proteins,
a reaction catalyzed by aminoacyl-tRNA protein transferases. The aminoacyl-tRNA protein transferase in eubacteria like
Escherichia coli is L/F transferase. Recent investigations have reported unexpected observations regarding the L/F transferase
catalytic mechanism and its mechanisms of substrate recognition. Additionally, recent proteome-wide identification
of putative in vivo substrates facilitates hypothesis into the yet elusive biological functions of the prokaryotic N-end rule
pathway. Here we summarize the recent findings on the molecular mechanisms of catalysis and substrate recognition by
the E. coli L/F transferase in the prokaryotic N-end rule pathway.
Keywords: aa-tRNA, Dupli-GNAT superfamily, L/F transferase, N-end rule, non-ribosomal peptide bond formation, posttranslational
addition of amino acid.
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