Involved in the archaeal biosynthesis of heme. Catalyzes the methylation of carbons 2 and 7 of uroporphyrinogen-III (UROGEN) to yield precorrin-2. It does not catalyze the overmethylation of precorrin-2 to trimethylpyrrocorphin. 2 S-adenosyl-L-methionine + uroporphyrinogen III = H(+) + precorrin-2 + 2 S-adenosyl-L-homocysteine Porphyrin-containing compound metabolism; siroheme biosynthesis; precorrin-2 from uroporphyrinogen III: step 1/1. Homodimer. Belongs to the precorrin methyltransferase family.