Control of the tRNA-tufB operon in Escherichia coli. 3. Feedback inhibition of tufB expression by an EF-Tu with a deletion in the guanine-nucleotide-binding domain

The expression of tufB, one of the two EF-Tu-encoding genes in Escherichia coli, is under autogenous control. Feedback inhibition of tufB expression by plasmid-borne EF-Tu has been used to answer the question of whether or not the integrity of the guanine-nucleotide-binding domain of EF-Tu is required for the autoregulatory role of the factor protein. We show that a large deletion of tufB, causing the elimination of an 81-amino-acid segment from the plasmid-borne EF-Tu, does not abolish tufB repression. We conclude that the autoregulation of the cellular EF-Tu level is not dependent on an intact guanine-nucleotide-binding domain and does not require binding of GTP to EF-Tu. The repressor activity of the deletion derivative of EF-Tu can be measured despite a rapid disappearance of the (altered) mutant protein from the soluble cytoplasmic fraction of the cell. Degradation and assembly in larger complexes are responsible for this disappearance.