Expression of Bovine Cytochrome P450c17 cDNA in Saccharomyces cerevisiae

The nucleotide sequence of the translation initiation regions of 96 Saccharomyces cerevisiae mRNAs was compiled and compared. The entire 5' untranslated sequence of most mRNAs is very rich in A-residues. G-residues are underrepresented in the untranslated region. The AUG startcodon context appeared to be distinctly different from that of animal mRNAs, although an A-residue at -3 also occurs very frequently (81 percent) in yeast mRNAs. The prevailing codon 3' adjacent to the AUG is the UCU serine codon. All these features are more extreme in the highly expressed genes. Fifty percent of all highly expressed genes use the UCU serine codon as second triplet. In this group G-residues are completely absent in the 7 bases preceding the startcodon and an A-residue occurs at position -1 and -3 at a frequency of 89 percent and 100 percent, respectively. The abundance of A-residues throughout the leader suggests that unstructured mRNA is required for efficient translation initiation in yeast. The consensus sequence for the AUG context in highly expressed genes can be summarized as follows: (Sequence: see text).