Figure 1.

Short Interspersed Element (SINE) structures. (a) Representation of the structure of an Alu element of ~300 bp. Two monomers ancestrally derived from the 7SL RNA are separated from each other by an A-rich region with consensus sequence A₅TACA₆. Pol III transcription is driven by A- and B-box promoter elements located in the left arm which, together, form the binding site for TFIIIC. Another A-rich tract is located at the 3’ of the right arm, at the end of the Alu body. Pol III transcription is expected to terminate at the first encountered termination signal (Tn) which may be located at varying distances from the end of the Alu body, thus allowing for the generation of Alu RNAs having 3’ tails of different lengths and sequences. (b) Representation of the structure of a mammalian-wide interspersed repeat (MIR) of ~260 bp. A tRNA-related region, containing A- and B-box promoter elements and a Long Interspersed Repeat (LINE-related fragment are separated by Core-SINE, a highly conserved central sequence. The unique genomic region downstream of the 3’ end of the MIR element (dashed line) could contain the Pol III termination signal (Tn) which may be located at varying distances from the end of the MIR body. Adapted from [18,19].