DIFFERENTIAL REGULATION OF 2 MYOINOSITOL TRANSPORTER GENES OF SACCHAROMYCES-CEREVISIAE

We previously isolated two distinct Saccharomyces cerevisiae myo-inosi tol transporter genes, ITR1 and ITR2 (Nikawa et al., 1991). Here, we s tudied the regulation of their expression by measuring steady-state mR NA levels and beta-galactosidase activities of lacZ fusion genes under different conditions. The results show that the expression of the two ITR genes is differently regulated: ITR1 was repressed by inositol an d choline whereas ITR2 was constitutive. Deletion analysis of the ITR1 upstream region and comparison with the upstream regions of other gen es involved in phospholipid synthesis indicate that the octamer sequen ce 5'-TTCACATG-3' is important for the expression and inositol/choline regulation of the ITR1 gene.