E. Reifenberger et al., IDENTIFICATION OF NOVEL HXT GENES IN SACCHAROMYCES-CEREVISIAE REVEALSTHE IMPACT OF INDIVIDUAL HEXOSE TRANSPORTERS ON GLYCOLYTIC FLUX, Molecular microbiology, 16(1), 1995, pp. 157-167
In Saccharomyces cerevisiae, hexose uptake is mediated by HXT proteins
which belong to a superfamily of monosaccharide facilitators. We have
identified three more genes that encode hexose transporters (HXT5, 6,
7), Genes HXT6 and HXT7 are almost identical and located in tandem 3'
adjacent to HXT3 on chromosome IV, We have constructed a set of conge
nic strains expressing none or any one of the seven known HXT genes an
d followed growth and flux rates for glucose utilization. The hxt null
strain does not grow on glucose, fructose or mannose, and both glucos
e uptake and flux rate were below the detection level. Expression of e
ither HXT1, 2, 3, 4, 6 or 7 is basically sufficient for aerobic growth
on these sugars. In most of the constructs, glucose was the preferred
substrate compared to fructose or mannose. There is a considerable va
riation in flux and growth rates with 1% glucose, dependent on the exp
ression of the individual HXT genes. Expression of either HXT2, 6 or 7
in the null background is sufficient for growth on 0.1% glucose, whil
e growth of strains with only HXT1, 3 or 4 requires higher (greater th
an or equal to 1%) glucose concentrations. These results demonstrate t
hat individual HXT proteins can function independently as hexose trans
porters, and that most of the metabolically relevant HXT transporters
from S. cerevisiae have been identified.