Genetic Control of the Esterases I N the Protozoan Tetra

Two years ago Markert and Mbller (1959) introduced the concept of an isozyme, which they defined as one of the different molecular forms of an enzyme. They proposed that each isozyme could be controlled by a separate gene or that an isozymic series could be controlled by a single gene. Essentially the problem centers on the way in which genes control a protein: how a protein is made and how it is modified in structure and function under the influence of genotypic and microecological factors. According to the present genetic dogma the deoxyribose nucleic acid (DNA) code is translated into a ribose nucleic acid (RNA) code which specifies the sequence of amino acids in a polypeptide (see Watson, 1960; Ingram, 1960; Spiegelman, 1960). These sequences automatically determine the secondary and tertiary structures of a protein. Analysis of the genetic control of an isozyme would, therefore, further our understanding of these relationships. Tetrahymena pyriformis possesses several different esterases, some of which form an isozymic series (Allen, 1960a). Although this study suggested that the series might be under the control of a single locus, only recently has a definitive answer been obtained. This report will present these observations and also evidence for the genetic control of other members of the family of esterases. The behavior of the isozymes in heterozygotes suggests that they are also under epigenetic control (Nanney, 1958) and that the pattern of nuclear differentiation and vegetative assortment is probably similar to that observed for other loci in this organism.