Analysis of the THR4 region on chromosome III of the yeast Saccharomyces cerevisiae

The gene encoding threonine synthase (THR4) from the yeast Saccharomyces cerevisiae was cloned by complementation of a thr4 mutant. This gene was also found on a lambda clone (5239) consisting of a fragment of chromosome III inserted in the vector lambdaMG3. The THR4 gene encodes a protein of 514 amino acids (M.W. 58 kDa), which has extensive homologies with E. coli threonine synthase (thrC) and B subtilis threonine synthase. The 5' flanking region of the gene contains three regulatory sequences TGACT(C)] for the general amino acid control (GCN). About 130 bp downstream of the THR4 gene another large open reading frame (563 amino acids) is found in the opposite orientation. This may imply that this open reading frame, called CTR86, shares a terminator region with THR4. The function of the protein encoded by CTR86 is not yet clear, but the fact that the upstream region contains a GCN4 responsive site suggests that the gene product may also be involved in amino acid biosynthesis.