Isolation and characterization of a SCT1 gene which can suppress a choline-transport mutant of Saccharomyces cerevisiae.

The yeast Saccharomyces cerevisiae possesses a choline-transport system encoded by the CTR1 gene. We isolated a yeast gene, SCT1, that can suppress a CTR1 defect when introduced as a multicopy. The SCT1 coding frame is capable of encoding 759 residues with a calculated molecular weight of 85,734. On Northern blot analysis, an RNA species that hybridized with the coding region was detected in the total RNA of the wild-type yeast. The transcription of SCT1 is constitutive. The primary translation product contains three membrane-spanning domains, a PEST-like sequence, and a glutamic acid-rich sequence at the C terminal end. Gene disruption experiments showed that SCT1 is not an essential gene under the standard culture conditions. SCT1 did not suppress a null mutant of ctr1, indicating that a mutant form of choline transporter is necessary for the suppression caused by SCT1.