Gene Expression in Heterozygotes

IN many cases a gene appears to function only by synthesizing a polypeptide chain through the mediation of ribonucleic acid (RNA), and hence controlling the synthesis of a protein. A mutation may cause a different polypeptide chain to be synthesized, for example, in the hæmoglobinopathies, or may result in failure to produce a polypeptide chain at all. In man there is little variation, in most individuals, of the concentration of each of the various proteins in the body fluids. This suggests that the rate of synthesis of each protein is controlled by the concentration already present. If this is so, a process of feed-back repression must operate. This may be at gene-level, perhaps resembling the regulator gene and represser mechanism of bacteria 1 , or at RNA-level. It is suggested that, in suitable cases, a study of the concentration of a protein or enzyme in the heterozygote may help to decide which type of mutation is involved.