A novel approach to cloning transcriptionally active retrovirus-like genetic elements from mouse cells

A family of dispersed, moderately repeated mouse genetic elements is expressed as retrovirus-like 30S RNA species (VL30 RNA) which can be transmitted to other cells when packaged as a pseudovirion complex by murine leukemia viruses (MuLV). Using the endogenous reverse transcriptase reaction of VL30 RNA-containing MuLV particles, full-length VL30 DNA was synthesized and cloned in pAT153. Analysis of a number of clones identified long terminal repeat structures (LTRs) characteristic of retrovirus proviruses and transposable genetic elements. Whilst the unique region of all clones was identical, the LTRs displayed some heterogeneity. Comparison of the unique region of cloned VL30 DNA with mouse genomic VL30 sequences showed the retrovirus-derived clones to be encoded by only a few members of the divergent VL30 gene family. These findings thus demonstrate a method for cloning a defined sub-class of retrovirus-like cellular genes which are both transcriptionally active and transmissible by a retrovirus.