The genes of all these RNAs (as well as the corresponding SINEs) have an internal pol III promoter. The promoter in tRNA and 7SL RNA genes consists of two boxes (A and B) of about 11 nt spaced by 30–35 nt, while the 5S rRNA genes have three such boxes: A, IE and C ( Schramm and Hernandez, 2002 ). The presence of the promoter within the transcribed sequence is critical for SINE amplification, as the promoter is preserved in new SINE copies. By the head structure, SINEs are divided into three types according to the RNA of origin (tRNA-, 7SL- and 5S rRNA-derived; Figure 1 ).