Transcriptional analysis of Ty1 deletion and inversion derivatives at CYC7.

One class of Ty insertion mutation in Saccharomyces cerevisiae activates expression of adjacent structural genes. The CYC7-H2 mutation, in which a Ty1 element is inserted 5' to the iso-2-cytochrome c coding region of CYC7, causes a 20-fold increase in CYC7 expression. Deletion analysis of CYC7-H2 has shown that distal regions of the Ty1 element are not essential for the transcriptional activation at CYC7. In this report, we have analyzed Ty1 and CYC7 RNA from two CYC7-H2 deletion derivative genes to determine whether a direct correlation exists between transcription of Ty1 and transcription of the adjacent gene. Assuming that all Ty1 elements in the genome are transcribed equally, amounts of CYC7-H2 deletion derivative Ty1 RNA were found to be at least fivefold lower than the amount estimated for the average Ty1 element. These same Ty1 deletion derivatives caused a 20-fold increase in adjacent CYC7 expression. This finding suggests that the mechanism by which Ty1 activates adjacent gene expression does not require normal levels of Ty1 transcription. Two inversion derivatives of the CYC7-H2 Ty1 have also been analyzed. These derivatives did not produce any iso-2-cytochrome c or any normal CYC7 mRNA. Instead they were found to produce a Tyl-CYC7 fusion RNA. Consistent with our findings on CYC7-H2 Ty1 transcription, the amount of the fusion RNA was very low. In addition, the Ty1 inversion derivatives produced a new RNA that mapped to sequences upstream from the inverted Ty1 segment. Similar to Ty1 insertions that activate transcription, the new RNA was found to be transcribed away from Ty1.