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pubmed:abstractText |
Transcription of the HIS4 gene begins at a single site (I) at position -60 from the ATG that begins translation. We have made linker insertions/deletions in the 5' noncoding region to identify the elements required for the specificity of transcription initiation. Although there are four sequences that begin TATA and are near the start of transcription (-170, -132, -123, and -102) only the sequence at -123 (TATA-123) is required for transcription initiation. By inserting synthetic oligonucleotides into a mutant from which TATA-123 had been deleted, we found that just TATA or TATAA does not work but that TATAAA functions almost as well as the wild-type sequence. This hexamer does not work in the opposite orientation (TTTATA). When a synthetic TATA sequence is placed upstream from the normal site, the site of initiation also moves upstream in a roughly cometric way even when TATA-123 is present. Analysis of transcripts in strains where the distance between the TATA sequence and the wild-type site of transcription initiation (I site) has been altered shows that in yeast, unlike higher cells, transcription does not initiate at a strictly defined distance from the TATA sequence. Constructions that alter the distance between the TATA and the I site or remove the I site change the pattern of transcription initiation without affecting the level of HIS4 expression. Deletions that eliminate the I site produce heterogeneous transcripts and deletions that substantially shorten the distance between TATA-123 and the I site initiate at multiple sites downstream from the I site. Thus, both the TATA and the sequences downstream from it determine the pattern of transcription initiation.
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