Multifunctional enzyme that catalyzes the SAM-dependent methylations of uroporphyrinogen III at position C-2 and C-7 to form precorrin-2 via precorrin-1. Then it catalyzes the NAD-dependent ring dehydrogenation of precorrin-2 to yield sirohydrochlorin. Finally, it catalyzes the ferrochelation of sirohydrochlorin to yield siroheme. 2 S-adenosyl-L-methionine + uroporphyrinogen III = H(+) + precorrin-2 + 2 S-adenosyl-L-homocysteine NAD(+) + precorrin-2 = 2 H(+) + NADH + sirohydrochlorin 2 H(+) + siroheme = Fe(2+) + sirohydrochlorin Cofactor biosynthesis; adenosylcobalamin biosynthesis; precorrin-2 from uroporphyrinogen III: step 1/1. Cofactor biosynthesis; adenosylcobalamin biosynthesis; sirohydrochlorin from precorrin-2: step 1/1. Porphyrin-containing compound metabolism; siroheme biosynthesis; precorrin-2 from uroporphyrinogen III: step 1/1. Porphyrin-containing compound metabolism; siroheme biosynthesis; siroheme from sirohydrochlorin: step 1/1. Porphyrin-containing compound metabolism; siroheme biosynthesis; sirohydrochlorin from precorrin-2: step 1/1. In the N-terminal section; belongs to the precorrin-2 dehydrogenase / sirohydrochlorin ferrochelatase family. In the C-terminal section; belongs to the precorrin methyltransferase family.