strand are required for this to proceed to the elongation step. The process of transcribing during elongation is very fast. Elongation takes place until the RNA polymerase comes across a termination signal (terminator) which arrests the process and causes the release of both the DNA template and the new RNA molecule. The DNA usually encodes the termination signal. Eukaryotic transcription The majority of eukaryotic genes are transcribed by RNA polymerase II, proceeding in the 5' to 3' direction. In eukaryotes, specific subunits within the RNA polymerase II complex allow it to carry out multiple functions. General transcription factors help binding RNA polymerase II to DNA. Promoters are cites where RNA polymerase II binds to start transcription and, in eukaryotes, transcription starting point is positioned at +1 nucleotide. Like all RNA polymerases, it travels along the template DNA, in the 3' to 5' direction and synthesizes a new RNA strand in the 5' to 3' direction, by adding new bases to the 3' end of the new RNA. A transcription bubble occurs as a result of the double stranded DNA unwinding. After about 25 base pairs of the DNA double strand are unwound, RNA synthesis takes place within the transcription bubble region. Supercoiling is also part of this process since DNA regions in front of the RNA polymerase II are unwinding, while DNA regions behind it are rewinding, forming a double helix again. The RNA polymerase carries out the majority of the steps during the transcription cycle, especially in maintaining the transcription bubble open for the complementary base pairing. There are some steps of the transcription cycle that require more proteins, such as the Rpb4/7 complex and the RNA polymerase attached to the elongation factor transcription factor IIS (TFIIS). See also Transcription factors Transcription (genetics)#Pre-initiation References Genetics Gene expression