Analysis of the relA Gene Product of Escherichia coli

Open Access
Publisher Website
Google Scholar
Abstract
The relA gene product, ATP:GTP 3′-pyrophosphotransferase (stringent factor) has been isolated in homogeneous form from an Escherichia coli strain polyploid for this gene at a yield of 1 mg/100 g cells and at a specific activity in a ribosome-activated assay at 37 °C of 120 μmol guanosine pentaphosphate formed min−1 mg protein−1. The specific activity in a methanol-activated assay at 25°C was found to be 4 μmol guanosine pentaphosphate formed min−1 mg protein−1. These values are about 100 times higher than reported by others. Our further studies of this enzyme led to the following results. Antibodies raised against this enzyme inhibit the ribosome-activated synthesis of guanosine tetraphosphate and pentaphosphate but have no effect on the much slower synthesis, detected in the absence of ribosomes. The amount of stringent factor in the relA+ strain CP78 is estimated to about 1 copy per 200 ribosomes. The amount of antibody-binding material in CP79 (relA) is at least 5 times lower.