PROTEIN-SYNTHESIS IN BRUCELLA-ABORTUS INDUCED DURING MACROPHAGE INFECTION

Brucella abortus is a facultative, intracellular, pathogenic bacterium that replicates within macrophages and resists macrophage microbicida l mechanisms. To study gene expression and to elucidate the defense me chanisms used by B. abortus to resist destruction within macrophages, protein synthesis by B. abortus was examined by pulse-labeling techniq ues during intracellular growth within J774A.1, a macrophage-like cell line, Prominent changes observed include increased synthesis of Bruce lla proteins with estimated molecular masses of 62, 28, 24, and 17 kDa . The 62-kDa protein was identified by immunoprecipitation analysis as Hsp62, a GroEL homolog. A protein of 60 kDa was expressed during acid shock and may represent a modified form of Hsp62. The 28- and 17 kDa proteins have not been observed under any in vitro stress condition an d presumably represent macrophage-specific induction, The 24-kDa prote in comigrates with an unidentified protein induced by acid shock, desi gnated Asp24. Expression of Asp24 is optimal at pH values below 4.0 an d within the first 3 h following a shift from pH 7.3 to 3.8, This corr esponds directly with a period of optimal bacterial survival at a redu ced pH and suggests an active role for this protein in resistance to s uch environments, The identification of these gene products and the me chanisms controlling their expression is an important step in understa nding the resistance of Brucella spp. to intracellular destruction wit hin macrophages.