The HERV-K Family of Human Endogenous Retroviruses
B Berkhout
Of the numerous endogenous retroviral elements that are present
in the human genome, the abundant HERV-K family is distinct because several
members are transcriptionally active and coding for biologically active
proteins. The HERV-K genome has been demonstrated to encode an active
dUTPase, protease, and endonuclease, and we now report the cloning of a
partially active RT enzyme. Inspection of the HERV-K sequences revealed
signs of recombination, a hallmark of exogenous retroviruses. Other genome
characteristics that were reported previously for actively replicating
retroviruses are also apparent for the endogenous HERV-K virus. In
particular, we observed suppression of the dinucleotide CpG that represents
potential methylation sites. We also were able to evaluate the mutational
spectrum of the HERV-K Reverse Transcriptase (RT) enzyme by comparison of 34
available sequences. Interestingly, this analysis revealed a striking similarity
with the properties of the HIV-1 RT enzyme, with a preference for G-to-A
transitions, which may explain the abundance of the A-nucleotide in the
retroviral genome of HIV-1 and HERV-K