Genetics of yeast hexokinase

Area of Science:

• Biochemistry
• Molecular Biology
• Yeast Genetics

Background:

• Hexokinases (EC 2.7.1.1) are crucial enzymes for glucose metabolism in Saccharomyces cerevisiae.
• Two major hexokinase isozymes, P1 and P2, are involved in yeast's ability to utilize sugars.
• Understanding the genetic basis of hexokinase activity is key to comprehending yeast metabolic pathways.

Purpose of the Study:

• To characterize two independent Saccharomyces cerevisiae mutants deficient in hexokinase activity.
• To identify and map the genes responsible for hexokinase isozymes P1 and P2.
• To elucidate the nature of mutations affecting hexokinase function and their impact on fructose utilization.

Main Methods:

• Isolation and characterization of Saccharomyces cerevisiae mutants lacking hexokinase activity.
• Genetic analysis including complementation tests and gene mapping.
• Analysis of spontaneous revertants to assess enzyme properties and gene linkage.
• Biochemical and immunological characterization of wild-type and mutant hexokinase enzymes.

Main Results:

• Two mutant strains, hxk1 and hxk2, were identified, both growing on glucose but not fructose.
• Genetic analysis revealed two unlinked, recessive, non-complementing genes (hxk1 and hxk2) controlling hexokinase isozymes P1 and P2, respectively.
• hxk1 is located on chromosome VIR and hxk2 on chromosome IIIR.
• Spontaneous revertants showed altered, more thermolabile enzymes, suggesting missense mutations in the structural genes for hexokinases P1 and P2.
• These hexokinases are likely essential for S. cerevisiae growth on fructose.

Conclusions:

• The hxk1 and hxk2 genes encode distinct hexokinase isozymes (P1 and P2) essential for fructose metabolism in Saccharomyces cerevisiae.
• Mutations in hxk1 and hxk2 are missense mutations affecting the structural genes for these enzymes.
• Independent genetic control and distinct chromosomal locations of hxk1 and hxk2 highlight the complex regulation of hexokinase activity in yeast.