[Molecular analysis of new human endogenous retroviruses]

The genome of normal, uninfected animal cells contains gene sequences which are closely related to exogenous, infectious retroviral species. These genomes are called endogenous retrovirus, which have been isolated from a variety of vertebrates. The endogenous retrovirus genomes are stable genetic entities that are inherited in Mendelian fashion. In this study, we found the existence of many related endogenous retroviruses in human genomes, by cross-hybridization with human endogenous retrovirus, ERV3 env region. The ERV3-related endogenous retroviruses also contained a variety of restriction fragment length polymorphism (RFLP). We carried out molecular cloning of four retroviral fragments among their endogenous retrovirus genomes. The four retroviruses were named SY-1, SY-2, SY-3 and SY-4, respectively. A single copy of SY-1, 2 and 3 was integrated in human genome, whereas multi-copies of SY-4 were integrated. In sequence comparison, all of the four retroviruses were homologous with ERV3 pol-env region. SY-1 was located only on Y chromosome, and had the homologous sequence with human endogenous retrovirus NP-2 on Y chromosome. The flanking sequence of SY-1 as well as NP-2 might have an important role on investigating the origin and differentiation of Y chromosome. SY-2 was homologous with the endogenous retroviruses of not only primates but lower mammals such as mouse. It is suggested that SY-2 might be integrated into mammalian genome in early stage of evolutional process. SY-3 was a fragments of endogenous retrovirus, containing a sequence having homologies to U3 small nuclear RNA and other moderately repetitive sequences within the envelope region. SY-3 existed only in the genomes of human and rhesus monkey, but not in those of lower mammals.