Geoffrey Turner1, Madalina Barbulescu1, Mei Su1,

Michael I. Jensen-Seaman2, Kenneth K. Kidd2, and





Einstein College of Medicine, Bronx NY and


University School of Medicine, New Haven, CT





the many genera of retroviruses that exist in the human germline, HERV-K appears

to be the most intact and the most recently acquired in human evolution.  Since

first entering the lineage of catarrhines at about the time of the

catarrhine-platyrrhine divergence, HERV-K appears to have been reinfecting the

human genome until very recently.


            Using a number

of molecular dating methods, we asked when the HERV-K proviruses that are in the

human genome today originally formed.  HERV-K proviruses mainly exist in three

forms, relatively intact, full-length viral genomes of which there are about 20

in the human genome today, partial viral genomes, and solo LTRs, a product of

intraviral homologous recombination.


            Using a method

to date the time of formation of the HERV-K solo LTRs in the human genome (that

far outnumber the full-length proviruses), we estimate that about 100 HERV-K

proviruses were fixed in the human genome since the human and chimpanzee

lineages diverged.  Most of these formed within the last 1.2 to 2.7 million

years, suggesting that HERV-K has been relatively active during this period of



Several of the full-length

proviruses present in the human genome today formed before the gorilla,

chimpanzee and human lineages separated.  One is present at the orthologous

positions in the gorilla and chimpanzee genomes, whereas humans contain an

intact preintegration site.  This provides an excellent example of a locus where

the gorilla and chimpanzee genomes are more like each other than like that of

humans.  At least 13 of the full-length HERV-K proviruses in the human genome

formed after the human and chimpanzee lineages diverged.  At least two formed

sufficiently recently that they exist allelically with the intact preintegration

sites and are present in only a fraction of humans today.  One of these

proviruses contains full-length open reading frames for all viral proteins. 

This is a good candidate to be a retrovirus that is capable of reinfecting

humans today.