HEMOGLOBIN MESSENGER RIBONUCLEIC ACID . DISTRIBUTION OF 9S RIBONUCLEIC ACID IN POLYSOMES OF DIFFERENT SIZES

Reticulocyte polysomes contain a ribonucleic acid (9S ribonucleic acid) having many of theproperties proposed for the hemoglobin messenger ribonucleic acid. If this 9S ribonucleic acid is the hemoglobin messenger ribonucleic acid its distribution in polysomes of different sizes should vary in a manner predicted by the polysome model. Polysomes are structures composed of various numbers of ribosomes attached to a single messenger ribonucleic acid. Thus a disome is two ribosomes andamessenger ribonucleic acid, a trisome is three ribosomes and a messenger ribonucleic acid, etc. The polysomal distribution of 9S ribonucleic acid was determined by isolating various ribosome fractions, namely- tri- and tetrasomes, penta-and hexasomes, and free 80S ribosomes by sucrose density gradient centrifugation. These fractions were treated with sodium dodecyl sulfate to dissociate the ribonucleic acid and protein, and the quantities of the various ribonucleic acids were analyzed by density gradient centrifugation. The tri- and tetrasomes contained an average of 3.1 ribosomes/9S ribonucleic acid and the penta- and hexasomes contained an average of 4.7 ribosomes/9S ribonucleic acid. This is in close agreement to the calculated values of 3.6 for the tri- and tetrasomes and 5.4for the penta- and hexasomes. In the free 80S ribosome fraction there was 10.7 ribosomes/9S ribonucleic acid. The observed distribution is in accord with the 9S RNA being the hemoglobin RNA. © 1969, American Chemical Society. All rights reserved.