title: Absence of mRNA for casein in free polysomes of lactating ewe mammary gland.
abstract: Total polysomal RNA or poly A- containing RNA extracted from free polysomes of lactating ewe mammary gland was unable to direct a significant synthesis of alpha-s- and beta-casein. Polyacrylamide gel electrophoresis of poly A- containing RNA revealed that the two major peaks of mRNA isolated from membrane-bound polysomes were not observed in mRNA isolated from free polysomes. Purified 125-I anti-alpha-s-casein could bind significantly to membrane-bound polysomes only. These data suggest that casein synthesis occurs almost exclusively on membrane-bound polysomes and that this specificity may be attributed to the presence of casein mRNAs on these polysomes and their absence from free polysomes.
mesh_terms: D000818:Animals; D002364:Caseins / Q000096:biosynthesis*; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D007457:Iodine Radioisotopes; D007774:Lactation; D008321:Mammary Glands, Animal / Q000378:metabolism*; D011132:Polyribosomes / Q000378:metabolism*; D011233:Precipitin Tests; D011247:Pregnancy; D011485:Protein Binding; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism*; D012335:RNA, Ribosomal / Q000378:metabolism*; D012756:Sheep
chemical_list: D002364:Caseins; D007457:Iodine Radioisotopes; D012333:RNA, Messenger; D012335:RNA, Ribosomal