ANOXIA-INDUCIBLE RAT VL30 ELEMENTS AND THEIR RELATIONSHIP TO RAS-CONTAINING SARCOMA-VIRUSES

VL30 elements are associated with cancer by their overexpression in ro dent malignancies, their induction in a fibroblast response to anoxia which shares features with the malignant phenotype, and their presence recombined into Harvey murine sarcoma virus (HaSV) and Kirsten murine sarcoma virus. These sarcoma viruses contain ras oncogenes flanked on both sides by retrotransposon VL30 element sequences, in turn flanked by mouse leukemia virus sequences. Three very basic questions have ex isted about the VL30 element sequences found in sarcoma viruses: (i) h ow did they become recombined, (ii) what are their exact boundaries, a nd (iii) why are they there? To help decipher the nature of VL30 eleme nts in sarcoma viruses, we examined VL30 clones isolated from an anoxi c fibroblast cDNA library and independently by polymerase chain reacti on cloning from rat cell DNA. Sequence comparisons with HaSV revealed that HaSV was formed by the substitution of 0.7 kb of VL30 sequences b y 0.9 kb of c-Ha-ras sequences, with this event possibly facilitated b y the presence of an identical Alu-like repeat found upstream of the 5 ' recombination point in both the VL30 element and c-Ha-ras. Recombina tion occurred 42 bases beyond the Alu-like sequences in VL30 and 1596 bases beyond them in c-Ha-ras, at position 926 of HaSV. The 3' ras-VL3 0 recombination event in HaSV occurred within a seven-base region of s hared sequence identity, between HaSV bases 1825 and 1831. Recombinati on between Moloney leukemia virus (MoLV) and VL30 appears to have occu rred at a point corresponding to base 218 or 219 of MoLV and was near a TAR-like VL30 sequence; such recombination at the 3' end was between positions 7445 and 7456 of MoLV (HaSV positions 4694 to 4703). Kirste n murine sarcoma virus was found to be closely analogous to HaSV, and limited similar features were also seen with Rasheed sarcoma virus.