Congenital erythropoietic porphyria, for example, prematurely ... Uroporphyrin I, coproporphyrin I, and other symmetric .
initiation is the beginning of transcription. it occurs when the enzyme rna polymerase binds to a region of a gene called the promoter. this signals the dna to unwind so the enzyme can ''read'' the bases in one of the dna strands. the enzyme is now ready to make a strand of mrna with a complementary sequence of bases.