Palatinose Element of the Receptor of the Melezitose Locus in Saccharomyces

Abstract

THE receptor^1,2 of the melezitose (MZ) gene-system comprises at least five ‘elements’ corresponding to five α-glucosidic inductors of the enzyme melezitase, an α-glucosidase capable of splitting the five different α-glucosidic inductors of MZ, namely, turanose, maltose, sucrose, α-methyl-glucoside and melezitose^3,4. The totipotent allele, which responds adaptively to all five substrates, is designated MZ^TMSGZ (abbreviated to TMSGZ). Partially recessive alleles, for example, TMSGz, TMSgz, TMsgz, Tmsgz, and the totally recessive allele, tmsgz, were obtained by ultra-violet irradiation⁵. (The small letters indicate specific inabilities of cultures to respond adaptively to the corresponding substrates.) The multiple alleles are inferred, on the receptor-hypothesis^1,2, to reflect mutations (heritable changes in folding) of the proteinaceous receptor, a component of the gene controlling the capacity to respond to different inductors. It is of special interest to know if the synthetic α-glucoside, palatinose (α-glucosido-6-fructofuranose), can act as a substrate and an inductor of this particular enzyme. Emeis⁶ has already shown that Saccharomyces cultures carry genes controlling the fermentation of palatinose, but since there are other genes which split α-glucosides (and fructofuranosides), and since he did not have genetically identified MZ cultures with which to make specific tests, further analysis was necessary to implicate MZ. The totipotent TMSGZ cultures of the Lindegren Breeding Stock are able to ferment palatinose after 48 h, but specific partial mutants, for example, TMsgz and recessive tmsgz cultures, do not ferment palatinose when tested on EMB-agar and by the Durham tube technique (remained negative for five days)⁷. The fact that the TMSGZ cultures fermented palatinose suggested that palatinose might be one of the substrates (and possibly an inductor) by which the different alleles of the MZ locus may be distinguished from each other.