Long Terminal Repeats of Human Endogenous Retrovirus K Family (HERV-K) Specifically Bind Host Cell Nuclear Proteins

Solitary long terminal repeats (LTRs) of the human endogenous retroviruses, scattered in several thousand copies throughout the human genome, are potentially capable of affecting the expression of closely located genes. To assess their regulatory potential, the LTR sequences of one of the most abundant HERV families (HERV-K) were screened for the presence of binding sites for the host cell nuclear factors using mobility shift and UV-crosslinking assays. It was shown that the LTR sequences of two subfamilies harbor a specific binding site for a complex consisting of at least three proteins, ERF1, ERF2 and ERF3 of 98, 91 and 88 kDa apparent molecular mass, respectively. This binding site is located in the 5' region of the LTR U3 element. The preservation of the specific protein binding site in different HERV-K LTR sequences suggests their possible role in regulation of nearby located genes.