Genetic control of nucleoside transport in sheep erythrocytes

Nucleoside transport in sheep erythrocytes is under the genetic control of two allelomorphic genes (NuI and Nui), where NuI codes for the functional absence of a high-affinity nucleoside transport system and is dominant to the gene (Nui) coding for the presence of the transport system. Kinetic and inhibitor experiments show that the high-affinity transport system is not present in heterozygous erythrocytes, demonstrating that the NuI gene is completely dominant over the Nui gene. It is suggested that the Nu locus may not represent the structural gene locus of the nucleoside transport system. Instead, it may be a regulator gene locus.