| Approximately one quarter of human DNA has been generated by the continuous retroposition of L1 long interspersed elements (LINEs) and Alu short interspersed elements (SINEs). The autonomous L1 elements are the major source of insertional mutagenesis, a potentially hazardous cellular process with fundamental evolutionary implications. The non-autonomous Alu elements are believed to efficiently exploit the L1 retroposition machinery for their own propagation. The mechanistic details by which the two L1 proteins mediate target DNA cleavage and genomic re-insertion of associated RNA via reverse transcription are unclear. It is equally obscure how Alu ribonucleoprotein particles (RNPs) might recruit L1 encoded protein(s) for genomic re-integration of Alu RNA. We plan to use X-ray crystallography to provide essential structural details on components and sub-complexes of the L1 retroposition machinery. We also plan to establish a cell-free translation/retroposition assay to test if Alu RNPs are indeed substrates for L1 protein(s). The results should help to position L1 elements and non-LTR retroposons in general, in the evolutionary context of mobile genetic elements. They should also allow us to relate retroposition to processes like the action of telomerase, which contains a reverse transcriptase similar to the one encoded by L1. Furthermore we aim to gain insight into how to potentially manipulate retroposition in cancer cells that express a high level of L1 and Alu RNAS. |
