title: Identification of novel endogenous betaretroviruses which are transcribed in the bovine placenta.
abstract: Sequences of retroviral origin occupy approximately 10% of mammalian genomes. Various infectious endogenous retroviruses (ERVs) and functional retroviral elements have been reported for several mammals but not cattle. Here, we identified two proviruses, designated bovine endogenous retrovirus K1 (BERV-K1) and BERV-K2, containing full-length envelope (env) genes in the bovine genome. Phylogenetic analysis revealed that they belong to the genus Betaretrovirus. By reverse transcription (RT)-PCR, both BERV-K1 and -K2 env mRNAs were detected in the placenta and cultured bovine trophoblast cells. Real-time RT-PCR analysis using RNAs isolated from various bovine tissues revealed that BERV-K1 env mRNA was preferentially expressed in the placenta. Moreover, we also found the expression of doubly spliced transcripts, named the REBK1 and REBK2 genes. Both the REBK1 and REBK2 proteins have motifs for a putative nuclear localization signal and a nuclear export signal. REBK1 and REBK2 fused with green fluorescent proteins were localized mainly in the nuclei when they were expressed in bovine and porcine cells. In the env and 3' long terminal repeats of BERV-K1 and -K2, we found regulatory elements responsible for the splicing and transport of viral RNAs and/or translation of the env genes. Although we have not identified the expressed Env proteins in bovine tissues, these data suggest that both BERV-K1 and BERV-K2 express Env proteins and that these proteins may have physiological functions in vivo.
authors.affiliation: Laboratory of Signal Transduction, Department of Cell Biology, Institute for Virus Research, Kyoto University, 53 Shogoin-Kawaracho, Sakyo-ku, Kyoto-city, Kyoto 606-8507, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Baba
authors.forename: Yuki
authors.initials: Y
authors.lastname: Nakaya
authors.forename: Takayuki
authors.initials: T
authors.lastname: Shojima
authors.forename: Yoshikage
authors.initials: Y
authors.lastname: Muroi
authors.forename: Keiichiro
authors.initials: K
authors.lastname: Kizaki
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Hashizume
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Imakawa
authors.forename: Takayuki
authors.initials: T
authors.lastname: Miyazawa
mesh_terms: D000818:Animals; D030121:Betaretrovirus / Q000235:genetics / Q000302:isolation & purification*; D002353:Carrier State / Q000662:veterinary*; D002417:Cattle; D002478:Cells, Cultured; D016000:Cluster Analysis; D004279:DNA, Viral / Q000737:chemistry / Q000235:genetics; D020077:Endogenous Retroviruses / Q000235:genetics / Q000302:isolation & purification*; D005260:Female; D008969:Molecular Sequence Data; D010802:Phylogeny; D010920:Placenta / Q000821:virology*; D011247:Pregnancy; D012367:RNA, Viral / Q000032:analysis / Q000235:genetics; D012192:Retroviridae Infections / Q000662:veterinary*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D017385:Sequence Homology; D014158:Transcription, Genetic; D014327:Trophoblasts / Q000821:virology
chemical_list: D004279:DNA, Viral; D012367:RNA, Viral