MESSENGER-RNA ATTACHMENT TO ACTIVE RIBOSOMES

Abstract
Attachment of messenger-RNA to 100 S and 70 S ribosomes results in "heavy" 100 S (70 S) ribosomes which sediment faster than free ribosomes. Many, if not all, "heavy" ribosomes are also "active"; that is, capable of functioning as sites for protein synthesis. Only a small fraction (5-10%) of total ribosomes are "heavy" ("active"). Thus, it appears that, at any given moment, only a correspondingly small ribosome fraction functions in protein synthesis.