Delta sequence of Ty1 transposon can initiate transcription of the distal part of the URA2 gene complex in Saccharomyces cerevisiae.

Expression of a silent aspartate transcarbamylase (ATCase) domain can occur by insertion of a Tyl retrotransposon within the coding sequence of a mutated ura2 allele. This unusual type of Ty-mediated gene activation is possible as the URA2 gene product is a multifunctional protein containing the carbamoyl phosphate synthetase (CPSase), the ATCase and a cryptic dihydroorotase (DHOase) domain. The region in which transcription of the corresponding allele is initiated was determined by RT-PCR experiments. Expression is initiated by a sequence located in the delta element of the Tyl and not by a sequence of the URA2 gene itself. This situation differs with the Ty-mediated gene activation described thus far, in which the transposon substitutes only the 5' regulatory sequences and in which the normal transcription start point is used. The corresponding protein carries both the DHOase-like domain and the ATCase domain, suggesting that the DHOase-like domain is at least involved in the architecture of the protein and necessary to render the ATCase domain functional.