The synthesis of fatty acid synthetase on free polyribosomes from lactating rabbit mammary gland was demonstrated by using polyribosomes run-off techniques and immunochemical identification of products with synthetase antiserum. Several reproducible and discrete immunoprecipitable polypeptides were observed which were within the molecular-weight range of the synthetase subunit (235 000--252 000), as well as several of lower molecular weight.
