Ferritin mRNA is found on bound as well as on free polyribosomes in rat heart.
Free and endoplasmic reticulum-bound polyribosomes from rat heart were examined for their ferritin mRNA content. A procedure for separation and purification of the two ribosome populations that produced good yields of homogeneous mono- and polyribosomes with no contaminating ultrastructures and gave distinctive sedimentation profiles in 15-50% sucrose gradients was developed. 14C-labeled free and bound polyribosomes added to heart preparations indicated that only 3% of free and 5.5% of bound polyribosomes cross-contaminated the bound and free fractions, respectively. RNA from both polyribosome populations hybridized with [32P]cDNA for rat ferritin. The extent of hybridization with mRNA from endoplasmic reticulum (ER)-derived polyribosomes was much greater than what could be accounted for by cross-contamination with free polyribosomes. This indicates that heart ferritin is synthesized not only on free polyribosomes for internal use in iron storage but also on ER-bound polyribosomes, where it may be destined for secretion into the plasma.
Department of Chemistry and Biochemistry, California State University, Fullerton 92634.
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Campbell
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Ismail
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Linder
D000818:Animals; D002499:Centrifugation, Density Gradient; D005260:Female; D005293:Ferritins / Q000235:genetics*; D008099:Liver / Q000032:analysis / Q000648:ultrastructure; D008854:Microscopy, Electron; D009206:Myocardium / Q000032:analysis* / Q000648:ultrastructure; D009693:Nucleic Acid Hybridization; D012333:RNA, Messenger / Q000032:analysis*; D051381:Rats; D011919:Rats, Inbred Strains; D012270:Ribosomes / Q000032:analysis* / Q000648:ultrastructure
D012333:RNA, Messenger; D005293:Ferritins