DIFFERENTIAL TRANSCRIPTION OF THE 2 SACCHAROMYCES-CEREVISIAE GENES ENCODING ELONGATION-FACTOR-2

The single polypeptide chain of elongation factor 2 (EF-2) is encoded by two Saccharomyces cerevisiae genes (EFT1 and EFT2) with unique flan king sequences. One gene is necessary and either is sufficient for cel l viability. In the present work, we have analyzed the transcription o f EFT1 and EFT2. Although both genes harbor multiple transcription sta rt points, EFT1 initiates primarily at residue C at -39 and EFT2 at re sidue C at -37. Several candidate TATA boxes were identified in each g ene. Deletion analysis employing lacZ promoter fusions demonstrated th at the promoter for EFT2 is located within a 79-bp region beginning 33 5 nucleotides (nt) upstream from the start ATG codon. This region cont ains two overlapping sequences with homology to the consensus binding site for the yeast transcription factor, Rap1p/Grf1p/Tuf. In contrast, the sequences essential for the transcription of EFT1 were localized to the region between the start ATG and the stop codon of the VPS17 ge ne that terminates 267 nt upstream on the same strand. Analysis of pro moter strengths using lacZ fusions indicated that the promoter for EFT 2 is approx. 2.5-fold more active than that of EFT1. Analysis of the s teady-state levels of mRNAs revealed that EFT2 contributes approx. 70% of the total EF-2 mRNA while the remaining 30% is produced by EPT1. W e conclude that the difference in expression of EFT1 and EFT2 is due t o the differential transcription of their promoters.