Transcription is the process by which RNA is assembled from a DNA template. The two strands of the DNA double helix are held together by bonds between complementary base pairs. DNA encodes genetic information in the sequence of bases along one strand. The portion of the DNA molecule that is a single gene, or coding region, is bounded by termination and promoter sites. A molecule of RNA polymerase binds to the promoter site. It moves along the DNA separating the two strands of the double helix. Each now unpaired base will bind to a nucleotide in the vicinity that has the appropriate complementary base. In the synthesis of RNA, uracil is the nucleotide complementary to adenine. This process ceases when RNA polymerase reaches the termination site. The DNA strands bind to one another once again as the new RNA molecule moves away. This RNA is a copy, or transcript, of the message contained in the gene.