11-15 THE YEAST CELL 



We have extensive yeast pedigrees in which the SU/su genes 

 segregate regularly, producing offspring half of which are fermen- 

 ters of sucrose and raffinose and half of which are nonfermenters. 

 We also have stocks distinguished by their ability and inability to 

 ferment melibiose; ME su yeasts are incapable of fermenting raf- 

 finose. 



PRODUCTION OF CO2 WHEN DIFFERENT SUGARS ARE 

 USED IN THE FERMENTATION TUBES 



me su - - - 



Unless some evidence is forthcoming on differential permea- 

 bilities, these data indicate that (1) the hydrolysis of raffinose de- 

 pends on the presence of sucrase, which is capable of hydrolyzing 

 fructose from the raffinose molecule, leaving residual melibiose 

 (2) melibiase is not capable of hydrolyzing melibiose in the raf- 

 finose molecule, (3) the complete hydrolysis of raffinose depends 

 on the presence of both melibiase and sucrase, the latter acting 

 first. 



ALPHA GLUCOSIDES 



In methyl alpha glucoside, and maltose, glucose is linked to the 

 molecule by an alpha glucoside bond. Methyl alpha glucoside is 

 used as aa indicator of maltase because of the widely accepted view 

 that they are both hydrolyzed by the same enzyme. We have dis- 

 covered, however, that two different genes control the ability to 

 hydrolyze alpha methyl glucoside, and maltose. The gene control- 

 ling the hydrolysis of methyl alpha glucoside is segregated inde- 

 pendently of that controlling the hydrolysis of maltose. From het- 

 erozygous hybrids, we obtain four kinds of progeny with regard to 

 the fermentation of methyl alpha glucoside, and maltose: MG MA, 

 MG ma, mg MA, and mg ma. The MG ma and mg MA genotypes 

 are unexpected since methyl alpha glucosidase is supposedly capa- 

 ble of hydrolyzing both maltose and methyl alpha glucoside. It has 

 frequently been shown that enzyme extracts from yeast are capable 

 of hydrolyzing both substances in ui tro. The existence of this 

 variety of genotypes suggests either (1) that different or specifical- 

 ly modified enzymes control the hydrolysis of each of these alpha 

 glucosides or (2) that the genes involved control specifically differ- 

 ent permeabilities for the different alpha glucosides. It has also 

 been suggested that some disaccharides may be fermented directly 

 without hydrolysis. 



