Expression of the Silent Hemoglobin Gene in Sheep

Abstract We have analyzed the messenger ribonucleic acids from reticulocytes of adult sheep carrying different globin genes and synthesizing correspondingly different hemoglobins. Hemoglobin A (α2β2a) is synthesized by A/A homozygotes in the early stages of anemia, whereas these same animals switch over to hemoglobin C (α2β2c) synthesis when they are severely anemic. On the other hand, only hemoglobin B (α2β2b) is synthesized by normal or by anemic B/B homozygotes. All four types of sheep globin messenger ribonucleic acids (i.e. for α, βa, βb, or βc chains) are successfully translated in a protein-synthesizing lysate from rabbit reticulocytes. The newly synthesized radioactive sheep globin chains are separated from the rabbit globin chains by chromatography on a carboxymethylcellulose column. The results suggest that a switch from βa to βc messenger ribonucleic acid accompanies the development of anemia in A/A sheep. However, the rabbit reticulocyte lysate system synthesizes sheep globin chains in different proportions than they are synthesized intracellularly; in the rabbit lysate, α and βa chains constitute a lower percentage and βc chains a larger percentage of the synthesis. The method of Lodish (Lodish, H. F. (1971) J. Biol. Chem. 246, 7131) was used to quantitate the relative levels of α, βa, and βc messenger ribonucleic acids in reticulocytes from an A/A homozygote. The proportion of βc messenger is approximately twice as high as the proportion of βc synthesis in sheep reticulocytes. On the contrary, the proportion of α messenger is lower than the proportion of α chain synthesis in sheep reticulocytes.