Structural analysis of the 5' regions of yeast SUC genes revealed analogous palindromes in SUC, MAL and GAL.

In the yeast Saccharomyces cerevisiae six unlinked structural genes for invertase, the SUC genes, are known. We sequenced about 800 bp of the 5' non-coding region and the first 220 bp of the coding region of the genes SUC1, SUC3, SUC4 and SUC5 and compared them with the previously sequenced genes SUC2 and SUC7 (Sarokin and Carlson 1985a). All are highly homologous within the coding region but in the non-coding region SUC1 shows some differences and SUC2 is more highly diverged. Two different kinds of TATA boxes were identified: the more strongly expressed genes SUC1, 2 and 4 have the sequence TATAAA and the more weakly expressed genes SUC3, 5 and 7 have TACAAA. Though the SUC1 sequence is in general more homologous to the other SUC genes, the region between -140 and +100 of SUC1 is nearly identical to SUC2. This could be due to a gene conversion between SUC1 and the silent suc2 degrees allele which occurs in the strains carrying SUC1. Within the upstream regions of all the SUC genes three regions with palindromic sequences analogous to stem and loop structures were identified. Comparable structures could be detected in similar positions in the upstream sequences of the divergently transcribed yeast gene pairs MAL6S-MAL6T and GAL1-GAL10. Implications for the importance of these structures in the regulation and initiation of transcription are discussed.