A region internal to the coding sequences is essential for transcription of the yeast Ty-D15 element

The major transcript of the yeast transposable element Ty1 has its 5' end in one delta and the 3' end in the opposite delta, the direct repeats of about 335 base pairs (bp) at each end of the element. The transcriptional initiation signals of the Ty-D15 element that give rise to this transcript were found to have a number of unusual characteristics. The 5' delta by itself, which contained the initiation site for Ty transcription, gave no detectable transcription. A region internal to the transcript in a translated part of the element and about 140 bp downstream of the 5' delta was essential for initiation of the major Ty transcript. This internal activating region (IAR) had several interesting properties. When the portion of the delta upstream of the initiation site was replaced with DNA fragments that did not by themselves act as promoters, initiation directed by the IAR still occurred at about the same position, 200 to 400 bp upstream of the IAR. If fragments containing the IAR were inverted, transcription could still occur. When 468 or 636 bp was inserted between the delta and the IAR, initiations occurred near the normal delta initiation site and in the inserted DNA. Therefore, the location and properties of transcription signals for Ty-D15 differ considerably from those expected for a yeast gene transcribed by RNA polymerase II.