Transcription continues until a termination series is reached. The most common termination signal is a GC-rich region which is a palindrome, followed by an AT-rich sequence. The RNA made from the DNA palindrome is self- complementary and so base pairs internally to form a hairpin structure rich in GC base pairs followed by four or more U residues shown in the figure. Though, not all termination sites have this hairpin structure. Those which lack such a structure require an additional protein, called rho (p), to help identify the termination site and stop transcription.