EXPRESSION OF HIGH-AFFINITY TREHALOSE-H-CEREVISIAE( SYMPORT IN SACCHAROMYCES)

The expression of the high-affinity trehalose-H+ symport was investiga ted in various Saccharomyces cerevisiae strains and culture conditions , Previous kinetic studies of trehalose transport in yeast have reveal ed the existence of st least two different uptake mechanisms: a high-a ffinity trehalose-H+ symport activity repressed by glucose, and a cons titutive low-affinity transport activity, a putative facilitated diffu sion process. Exogenously added trehalose was not an inducer of the hi gh-affinity transport activity, and a correlation between trehalose an d maltose uptake by yeast cells was found. Our results indicate that t he maltose-H+ symporters encoded by MAL11, MAL21, and MAL41 are not re sponsible for the trehalose transport activity. The analysis of both t rehalose and maltose transport activities in wild-type and in laborato ry strains with defined MAL genes showed that the trehalose-H+ symport er was under control of MAL regulatory genes, Our results also suggest that the recently characterized AGT1 gene of S. cerevisiae may encode the high-affinity trehalose-H+ symporter. During diauxic growth on gl ucose the transport activity was low during the first exponential phas e of growth, increased as glucose was exhausted from the medium, and d ecreased again as the cells reached the late stationary phase. This pa ttern was coincident with that of the intracellular levels of trehalos e, The strong correlation between these two parameters may be of physi ological significance during adaptation of yeast cells to stress condi tions. (C) 1998 Elsevier Science B.V.