The yeast FBP26 gene codes for a fructose-2,6-bisphosphatase

Sequencing of an open reading frame 450 bp downstream from the yeast VPS35 gene revealed a putative peptide of 452 amino acids and 52.7 kDa. The predicted amino acid sequence has 45% identity with the 55-kDa subunit of the 6-phosphofructo-2-kinase/fructose-2,6- bisphosphatase (EC 2.7.1.105/EC 3.1.3.46) from rat liver and 42% identity with 480 amino acids in the center of the recently reported 93.5-kDa subunit of yeast 6-phosphofructo-2-kinase (EC 2.7.1.105). The product of the new yeast gene is similar to the entire sequence of the bifunctional rat liver enzyme and, unlike yeast 6-phosphofructo-2-kinase, has the histidine residue essential for fructose-2,6-bisphosphatase activity. Extracts from a chromosomal null mutant strain, fbp26::HIS3, incubated in the presence of [2-32P]fructose 2,6-P2, lacked in autoradiograms the characteristic 56-kDa labeled band observed in wild-type. The same band was intensified 3-fold over wild-type level with the FBP26 gene introduced on multicopy in the fbp26::HIS3 background. A similar increase was found for fructose-2,6-bisphosphatase activity in the same extracts. The FBP26 gene did not cause detectable increase in 6-phosphofructo-2-kinase activity when introduced on multicopy in a pfk26::LEU2 mutant, indicating that its gene product is predominantly a fructose-2,6-bisphosphatase. Growth on glucose, fructose, galactose, pyruvate, and glycerol/lactate was not impaired in strains carrying the fbp26::HIS3 allele.