Isolation of an inhibitor of cell-free protein synthesis from Salmonella enteritidis.

Sonic extracts of Salmonella enteritidis, serotype enteritidis, contain a factor which inhibits eukaryotic cell-free protein synthesis tested on a rabbit reticulocyte lysate system and on a poly(U)-dependent system from Artemia salina embryos. The factor is heat-labile, does not diffuse through dialysis bags and is precipitated by ammonium sulphate. A 78% recovery of the factor was obtained in the 60-80 per cent ammonium sulphate saturation range, with a 3.3-fold purification. The factor binds to DEAE-cellulose. In the fraction eluted at 0.55 M NaCl, SDS-polyacrylamide gel electrophoresis shows only two protein bands (Mr 55,000 and 29,000). While the inhibitory activity on protein synthesis of the crude factor is fairly stable at 4 degrees C, it becomes very labile after DEAE-cellulose chromatography. The ID50 of the partially purified factor was less than 0.55 microgram (20-fold purification).