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Published July 1993 | Published
Journal Article Open

The N-End Rule in Escherichia coli: Cloning and Analysis of the Leucyl, Phenylalanyl-tRNA-Protein Transferase Gene aat


The N-end rule relates the in vivo half-life of a protein to the identity of its N-terminal residue. Distinct versions of the N-end rule operate in bacteria, fungi, and mammals. We report the cloning and analysis of aat, the Escherichia coli gene that encodes leucyl, phenylalanyl-tRNA-protein transferase (L/F-transferase), a component of the bacterial N-end rule pathway. L/F-transferase is required for the degradation of N-end rule substrates bearing an N-terminal arginine or lysine. The aat gene maps to the 19-min region of the E. coli chromosome and encodes a 234-residue protein whose sequence lacks significant similarities to sequences in data bases. In vitro, L/F-transferase catalyzes the posttranslational conjugation of leucine or phenylalanine to the N termini of proteins that bear an N-terminal arginine or lysine. However, the isolation and sequence analysis of a β-galactosidase variant engineered to expose an N-terminal arginine in vivo revealed the conjugation of leucine but not of phenylalanine to the N terminus of the β-galactosidase variant. Thus, the specificity of L/F-transferase in vivo may be greater than that in vitro. The aat gene is located approximately 1 kb from clpA, which encodes a subunit of ATP-dependent protease Clp. Although both aat and clpA are required for the degradation of certain N-end rule substrates, their nearly adjacent genes are convergently transcribed. The aat gene lies downstream of an open reading frame that encodes a homolog of the mammalian multidrug resistance P glycoproteins.

Additional Information

© 1993 American Society for Microbiology. Received 22 January 1993. Accepted 6 May 1993. We are grateful to our colleagues whose names are cited in this paper and to B. Bachman (Yale University) for the gifts of strains and plasmids. We thank 0. Lomovskaya for helpful discussions and comments on the manuscript. We also thank D. Siegle and R. Kolter for communicating their DNA sequence data prior to publication and for providing phages from their copy of the Kohara library. This work was supported by grants to A.V. from the National Institutes of Health (GM31530 and AG08991). T.E.S. is a Merck Fellow of the Helen Hay Whitney Foundation.

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