If you really want to understand what is known about DNA transcription, you will first get a 500 level background in cell biology and biochemistry. After reading Genomes 3 by TA Brown (very good) you will hav a 600 level understanding. Now at the 700 level, the reading is tougher and doesn't fit together very well. You will need to read "Epigenetics" by Allis et al, since other authors mostly ignore it and it is important. Next, learn some embryology, which should be in an appendix in Davidson, but isn't.

Now you are ready for Davidson's "The Regulatory Genome." It is difficult and poorly explained. The core material is in multi-page figures with multi-page captions. The combination of no legend for the diagramming conventions, and highly complex biology, will surprise you if you are used to readily-understood biology figures. The transcription regulation discussed is that of embryological development, which is rather different from the metabolic enzyme regulation discussed in cell biology and biochemistry. If you stop struggling with the details in the figures, and hold them at arm's length, you get a glimpse of the essence of developmental biology at the molecular level.

There is much that isn't covered -- heterochromatin, euchromatin, transcription differences between the sexes, the master timing mechanism, the role of noncoding DNA -- but this is the frontier. If you want that glimpse, you should learn the prerequesite material, and THEN read Davidson.