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 Ty1 retrotransposon within the coding sequence of a mutated ura2 allele. This unusual type of Ty-mediated gene activ ation is possible as the URA2 gene product is a multifunctional protei n containing the carbamoyl phosphate synthetase (CPSase), the ATCase a nd a cryptic dihydroorotase (DHOase) domain. The region in which trans cription 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 Ty1 and not by a sequence of the URA2 gene itsel f This situation differs with the Ty-mediated gene activation describe d 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 invo lved in the architecture of the protein and necessary to render the AT Case domain functional.