FUNCTIONAL-CHARACTERIZATION OF THE REPEATED UAS ELEMENT IN THE PROMOTERS OF THE INO1 AND CHO2 GENES OF YEAST

In yeast, INO1 and CHO2 gene expression is subject to repression in re sponse to inositol and choline supplementation. The response by both g enes to inositol is controlled by a single set of regulatory factors a nd the highly conserved and repeated UAS(INO) element (consensus: 5' C ATGTGAAAT 3') that is found in multiple copies in both promoters. Howe ver, none of the native elements found in the INO1 and CHO2 promoters constitutes an exact match to the consensus element and the functional ity of individual elements from these two promoters has not been teste d. In this study, the function of individual putative UAS(INO) element s from both promoters was tested by placing promoter fragments into a reporter construct which lacked a UAS element but contained the TATA e lement and start of transcription from the yeast CYC1 gene fused to th e Escherichia coli lacZ gene. In addition, a set of oligonucleotides c ontaining the consensus UAS(INO) element with the first position syste matically modified was also tested for UAS(INO) function. These studie s indicated that elements that contain a C or an A as the first base a t the 5' end are functional to varying degrees. The majority of potent ial UAS(INO) elements from the INO1 promoter were found to be inactive , whereas all of the elements from the CHO2 promoter tested were activ e. These results are discussed in light of the differential regulation of the two promoters.