Presence and phylogenetic analysis of HERV-K LTR on human X and Y chromosomes: Evidence for recent proliferation

The K group of human endogenous retroviruses (HERV-K) has been suggested to have a role in disease and has recently been shown to include long termina l repeat (LTR) elements that are human specific. Here we investigated the p resence of HERV-K LTRs on the human X and Y chromosomes with the use of PCR on a monochromosomal somatic cell hybrid DNA panel. We report twelve such sequences on the X chromosome and ten sequences on the Y chromosome. Phylog enetic analysis reveals that clones X2, 4, 5, 6, 7, 11, 15 from the X chrom osome and clones Y4, 5, 7, 10 from the Y chromosome are closely related to the human-specific members of Medstrand and Mager's cluster 9. The sequence of clone Y7 from the Y chromosome is identical with human-specific HERV-K LTR element (AC002350) from chromosome 12q24. The findings suggest recent p roliferation and transposition of HERV-K LTR elements on these chromosomes. Such events may have contributed to structural change and genetic variatio n in the human genome. We draw attention to evolutionarily recent changes i n homologies between X and Y chromosomes as a method of further investigati ng such transpositions.