Genomic distribution and transcription of solitary HERV-K LTRs.
The human genome contains a family of endogenous retroviruses, HERV-K, with sequence homology to the B-type mouse mammary tumor virus. We have now identified a single HERV-K LTR within the C-type-related human retroviral element S71. The HERV-K LTR is located in the antisense direction between the S71 gag and the pol gene, replacing the 5' half of S71 pol. A number of HERV-K LTR-related cDNA clones were detected by screening various human cDNA libraries with an S71 HERV-K LTR probe, indicating abundant transcription of HERV-K-related LTRs in human tissues. Sequence analysis of four cDNA clones revealed LTR sequences with a nucleotide identity of 70 to 90% with HERV-K10 LTR. Some HERV-K-related LTR sequences contain potential short open reading frames. The analyzed cDNA clones do not harbor any retroviral sequences other than those related to HERV-K LTRs. However, most of the solitary LTRs were found to be coexpressed with cellular sequences. Transcription of these LTRs is probably directed by external cellular promoters. We show that HERV-KLTR-like sequences entered the primate genome about 33-40 million years ago. We estimate the human genome to contain about 25,000 copies of HERV-K-related LTRs, which are distributed over most human chromosomes in an irregular manner.
Leib-Mösch
C
C
III Medizinische Klinik, Universität Heidelberg, Mannheim, Federal Republic of Germany.
Haltmeier
M
M
Werner
T
T
Geigl
E M
EM
Brack-Werner
R
R
Francke
U
U
Erfle
V
V
Hehlmann
R
R
D000818:Animals; D001483:Base Sequence; D006224:Cricetinae; D003412:Cricetulus; D004247:DNA; D004279:DNA, Viral / Q000032:analysis; D015894:Genome, Human; D006801:Humans; D006822:Hybrid Cells; D008969:Molecular Sequence Data; D012091:Repetitive Sequences, Nucleic Acid; D015183:Restriction Mapping; D012190:Retroviridae / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid; D014158:Transcription, Genetic
D004279:DNA, Viral; D004247:DNA