The genomic DNA organisation and evolution of a retrovirus-transmissible family of mouse (VL30) genetic elements.

The sequence organisation of endogenous VL30 elements in the mouse genome was investigated by using a cloned representative of a retrovirus-transmissible VL30 cDNA. The majority of dispersed VL30 sequences could be assigned to a proviral-like structure 5.2-5.3 kbp long and bounded by long terminal repeats (LTRs). The existence of a hierarchy of evolutionarily conserved elements was rather limited and sequence heterogeneity between different elements was randomly distributed. However, the retrovirus-transmissible class of VL30 element was found to represent a distinct minority subgroup distinguishable by restriction sites and size (4.6-4.9 kbp long). Analysis of sequence conservation showed that VL30 elements display a more rapid turnover than endogenous murine leukaemia virus-related proviral sequences, and that VL30 LTRs show the most limited evolutionary distribution. Although discrete subsets of VL30 unique sequence were conserved in different rodents, the location of conserved regions was found to be variable, arguing against the presence of a functionally conserved protein coding region. These observations support the hypothesis that high frequency recombination, probably occurring during reverse transcription and the accompanying processes of duplicative transposition and amplification, have been a major determinant in the mode of evolution of the VL30 gene family.