Host proteins, including specific transcription factors with binding sites near transcription start sites, are necessary for this specificity (32 - 33). (fruitfly.org)
However, it is still unknown where exactly transcription starts and which regularly recurring DNA segments, DNA modifications or structural modifications of the DNA are required to determine the start of transcription. (sciencedaily.com)
When mapped to the genome, they tell us not only about the level of expression for various genes, but also which transcription start sites were used. (massgenomics.org)