Perpetually mobile footprints of ancient infections in human genome.

Up to 1% of the human genome is represented by human endogenous retroviruses (HERVs) and their fragments that are likely footprints of ancient primate germ-cell infections by retroviruses that occurred 10-60 million years ago. HERV solitary long terminal repeats (LTRs) can be often met in close vicinity to functional genes. The LTRs comprise a set of regulatory sequences like promoters, enhancers, hormone responsive elements and polyadenylation signals that might come out as new regulatory signals to resident genes and thus change their regulation in evolution. Moreover, the LTRs have a potential for chromatin remodeling that can also modulate gene expression. This review describes the integration specificity and distribution of the HERVs and LTRs in the human genome and discusses possible functional consequences of their integration in the vicinity of genes.