OK. RNA Polymerase builds mRNA molecules that are complementary to the DNA template. The mRNA has to be synthesized in the 5'--> 3' direction (remember that new nucleotides are added by forming a phosphodiester bond between the 5'-phosphate of the newly recruited nucleotide and the free 3'-hydroxyl of the last nucleotide that was added to the growing mRNA strand). To accomplish this, the DNA template is read in the 3'--> 5' direction, so that as complementary ribonucleotides are added, the mRNA transcript grows in the 5'--> 3' direction, antiparallel to the template. The bases of the ribonucleotides added to the mRNA transcript are complementary to the bases of the deoxyribonucleotides of the DNA template. The complementary base pairings are the same as in double-stranded DNA, except that RNA does not have T; it uses U instead. So for each A in the template, the trascript will have a corresponding U. Reading the template in the 3'--> 5' direction, the transcript would start out: 5'-AUG. . . -3' Does that make sense? Hope this helps. Here's a cool link for you: http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.html