Henry Levin heads the Section on Eukaryotic Transposable Elements, which analyzes LTR retrotransposons and the integration of their cDNA into the chromosomes of host cells. Work focuses on the mechanisms that direct integration to specific chromosomal sites and the impact integration preferences have on the cell. Our studies of integration include inserts throughout the S. pombe genome that revealed pol II transcribed promoters are the primary targets of Tf1 integration. We adapted high throughput sequencing and developed new technology to sequence 1 million insertion sites. These experiments show that Tf1 has a preference for stress response promoters and the targeting of integration involves the DNA binding protein Sap1. We have also applied new methods to sequence 1 million integration sites of HIV-1 in cultured cells. These data led to the important discovery that the integrase of HIV-1 directs integration to highly spliced genes by interacting with splicing factors. We continue to develop novel methods for applying integration technology. For example, we developed a method called integration profiling that uses the transposon Hermes and deep sequencing to map the essential genes of S. pombe. We and other labs are using this method to identify genes with specific functions.