Frameshifting in the expression of the Escherichia coli trpR gene

The trpR gene of Escherichia coli carries an open reading frame that encodes the trp repressor, 108 amino acids long. Here we show that translation of an additional (+1) reading frame of trpR occurs both in vivo and in vitro. This results in the synthesis of a stable +1 frame polypeptide. Using site-specific mutagenesis, immunological techniques and amino acid sequencing we have found that the N-terminus of the +1 frame product and that of the known 0 frame product are identical but that their C-termini differ. Our results are discussed in relation to the role of natural frameshifting as a regulatory mechanism of gene expression in general, and with respect to tryptophan biosynthesis in particular.