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Long terminal repeats (LTR) of endogenous retroviruses com-prise about 8% of human genome. Typical LTR contains a set of regulatory elements: promoters, enhancers, polyadenilation sites, which can take part in neighbouring genes expression regu-lation. | Poster Presentations Abstracts POSTER PRESENTATIONS P1 Functional Genomics Proteomics and Bioinformatics P1-1 The influence of the HERV-K LTR on KIAA1245 subfamily gene expression N. Abrarova E. Stoukacheva T. Vinogradova and E. Sverdlov Laboratory of structure and function of human genes Institute of Bioorganic Chemistry Moscow RUSSIA Long terminal repeats LTR of endogenous retroviruses comprise about 8 of human genome. Typical LTR contains a set of regulatory elements promoters enhancers polyadenilation sites which can take part in neighbouring genes expression regulation. Earlier we have described a subfamily of closely related genes highly similar to the KIAA1245 mRNA part of which contains a HERV-K LTR in their structure whereas the other lacks it. Using this subfamily as a model for studying regulation of gene transcription we showed that LTR serves as an alternative promoter and possess high enhancer activity. Genes that contain LTR differ from genes lacking it in cell type specificity of transcription. We generated a series of successive 5 - and 3 -dele-tion mutants with a 200 bp increment and also two middle variants 200 and 400 bp in length Mid200 and Mid400 respectively . To determine promoter activity of LTR and its fragments they were cloned into pGL3-BV vector containing luciferase reporter gene. The full-sized LTR demonstrated high promoter activity in Tera1 and NT2 D1 cell lines. To determine the enhancer activity LTR and subfragments were cloned in pGL3-PV vector which has SV40 promoter in its structure besides luciferase gene. Transient transfections demonstrated that Mid200 fragment of the LTR exhibits high cell type specific enhancer activity. In Tera1 cell line it was comparable to the activity of universal SV40 enhancer. This fact allows to suggest that enhancer is localized in this region of the LTR. The analysis of transcription of KIAA1245 subfamily genes have shown that LTR-lacking gene Al592309 is not transcribed in Tera1 and NT2 D1 cell