A novel retroviruslike family in mouse DNA

In the course of structural analysis of VL30 DNA elements, a recombinant retroviruslike element was encountered that contained non-VL30 long terminal repeats (LTRs) flanking internal VL30 sequences. With the aid of this novel LTR sequence probe, we cloned several DNA elements that were apparently members of a new retroviruslike family. A particular DNA element representative of this family (designated GLN) was characterized. It was approximately 8 kilobase pairs long and contained LTRs that are 430 base pairs long. It possessed an unusual primer-binding site sequence that corresponds to tRNAGln and a polypurine tract primer that is adjacent to the 3' LTR. The nucleotide sequences of the LTRs and their adjacent regions (which together housed all cis-acting retroviral functions) were different from those of known retroviruses and retroviruslike families. The comparison of three different GLN LTR sequences revealed a marked heterogeneity of U3 sequences relative to the homogeneity of R and U5 sequences. We estimate that approximately 20 to 50 copies of GLN elements are dispersed in all species of mice. GLN-related LTRs, however, are present in a much higher copy number (1,000 to 1,500 per genome). Nucleotide sequences that are more distantly related to GLN DNA are present in multiple copies in DNAs of other rodents but not in nonrodent genomes.