Extracellular labeling of growing secreted polypeptide chains in Bacillus subtilis with diazoiodosulfanilic acid

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Abstract
Studies of the mechanism of protein secretion in a gram-positive bacterium, B. subtilis, yielded results very similar to those previously obtained with a gram-negative organism: nascent chains protruding from protoplasts could be labeled extracellularly; the labeled chains could be recovered on polysomes isolated from the membrane-polysome fraction; they could be released by puromycin, low Mg2+ or chain completion; the completed chains include a known secreted protein (.alpha.-amylase); and the ribosomes appear to be attached to membrane solely by their nascent chains. The reagent used for extracellular labeling, [125I]diazoiodosulfanilic acid, yielded severalfold more specific labeling of the nascent chains (7-10% of the total cellular labeling and 1/4-1/3 of that of the membrane-polysome fraction) than was obtained earlier with other nonpenetrating reagent.