Protein synthesis in cell-free extracts of Coxiella burnetti.

Abstract

Some aspects of protein biosynthesis were investigated in extracts of the obligate intracellular bacterium Coxiella burnetti. Sucrose gradient analysis revealed small quantities of 30S and 50S ribosomal subunits, few 70S ribosomes and no polysomes. Functional endogenous mRNA was not detected. In translation of exogenously added poly(U), extracts required Mg2+ (17 mM) and NH4+ (60 mM) for optimal polyphenylalanine synthesis; the optimum MG2+ requirement differed from that of Escherichia coli. The translation of coliphage Q beta RNA by C. burnetti extracts required Mg2+ (13 mM), NH4+ (60 mM) and an energy source for polypeptide synthesis, and was sensitive to chloramphenicol but not to cycloheximide. Under optimal conditions, the translation of Q beta RNA proceeded at a rate and to an extent equal to that obtained in a conventional E. coli system. Electrophoretic analysis of translation products made during incubation of C. burnetti extracts with polycistronic Q beta RNA revealed a major product with a molecular weight of about 14 000; this product co-electrophoresed with the coat protein extracted from Q beta phage propagated in E. coli. The results suggested that the extracellular form of the rickettsia-like organism, C. burnetti, possessed the full array of components necessary for the initiation, elongation and termination of polypeptides.