1. In bacteria, RNA polymerase binds a promoter via σ; in eukaryotes, RNA polymerase binds via a transcription factor complex. Bacterial RNA polymerase is regulated purely by σ, but eukaryotic RNA polymerase is regulated both by the TFs and by various gene regulatory proteins. Although promoters are similar, the bacterial promoter is highly conserved, whereas eukaryotic promoters are less so (and may not all be present).
2. RNAs can:
   • Bind specific RNA sequences and direct base-modifying proteins (snoRNA).
   • Catalyse their own excision (self-splicing introns).
   • Bind RNA sequences and catalyse their excision (snRNA in spliceosomes).
   • Bind RNA sequences and guide the insertion or deletion of bases (gRNA).
   • Self-binding can form protective tail structures (histone mRNA).
   • And don’t forget stem-loop terminators for RNA polymerase, and the ribosome.
3. In humans, DNA polymerase needs to synthesise 6 × 10⁹ basepairs (the entire genome) without error. And it does so: the error rate is about 10⁻⁹: so only about 6 mutations would be introduced during replication (which would almost certainly be in non-essential regions, since only 1.5% of the genome is transcribed). RNA polymerase only needs to transcribe a gene, which at most will be around 10⁴ nucleotides long, so again, most mRNAs will have either no errors, or only one, which given the redundancy of the genetic code, the plasticity of proteins, and that fact that the majority of the pre-mRNA transcript is intronic junk, is again unlikely to make the gene product non-functional.