Transcription and the strand that gets read
RNA polymerase reads the template strand three prime to five prime and therefore synthesises RNA five prime to three prime; the other strand is called the coding strand because its sequence matches the mRNA, with uracil replacing thymine. In prokaryotes RNA polymerase binds the promoter directly with a sigma factor, while eukaryotes require transcription factors to assemble at the TATA box before RNA polymerase II can bind — that difference is why eukaryotic transcription is so much more regulable. Eukaryotic pre-mRNA is then processed: a five prime cap and a poly-A tail are added for stability and export, and introns are removed by the spliceosome.