An Escherichia coli gene in search of a function

The rrnB gene of Escherichia coli is preceded by an open reading frame, which is cotranscribed with rrnB both in vivo and in vitro. It has earlier been shown that a 289 amino acid protein corresponding to this gene is actually synthesized in E. coli. In this paper we show that: (1.) The transcription of this gene diminishes the stringent response of the P1 promoter of the linked rrnB gene, but this is a cis effect and is not mediated by the protein product of the gene. (2.) The functional integrity of this gene seems to be essential, because efforts to replace it by a plasmid-coded copy mutagenized by Tn5 completely failed. (3.) The protein product of this gene was strongly overproduced by a recombinant plasmid, exploiting the principle of "translational coupling". This overproduction did not change the phenotype of the host cell significantly. The protein was purified to apparent electrophoretic homogeneity.