Identification of an internal ribosome entry segment in the 5 ' region of the mouse VL30 retrotransposon and its use in the development of retroviralvectors

Mouse virus-like 30S RNAs (VL30m) constitute a family of retrotransposons, present at 100 to 200 copies, dispersed in the mouse genome. They display l ittle sequence homology to Moloney murine leukemia virus (MoMLV), do not en code virus-like proteins, and have not been implicated in retroviral carcin ogenesis. However, VL30 RNAs are efficiently packaged into MLV particles th at are propagated in cell culture. In this study, we addressed whether the 5' region of VL30m could replace the 5' leader of MoMLV functionally in a r ecombinant vector construct. Our data confirm that the putative packaging s equence of VL30 is located within the 5' region (nucleotides 362 to 1149 wi th respect to the cap structure) and that it can replace the packaging sequ ence of MoMLV. We also show that VL30m contains an internal ribosome entry segment (IRES) in the 5' region, as do MoMLV, Friend murine leukemia virus, Harvey murine sarcoma virus, and avian reticuloendotheliosis virus type A. Our data show that both the packaging and IRES functions of the 5' region of VL30m RNA can be efficiently used to develop retrotransposon-based vecto rs.