Three kinds of human endogenous retrovirus-like sequences (HuERS-Pl, 2 and 3) were isolated from a HeLa cell genomic library using the 3′-half fragment of proline tRNA as a hybridization probe. These elements contained putative primer binding sites complementary to the 3′-terminus of proline tRNA and long terminal repeats (LTRs) characteristic of retrovirus provirus. The LTR sequence of HuERS-Pl consisted of about 690 nucleotides and contained a CAT box, a TATA box and a polyadenylation signal. A complete unit of an Alu family sequence was inserted into the 5′-LTR of one of the clones. HuERS-P2 also contained a TATA box and a polyadenylation signal in its LTR (about 840 nucleotides long), but the LTR sequence of this element was quite different from that of HuERS-Pl. Although clone HuERS-P3 contained only the 5′-LTR region, this LTR sequence contained a CAT box, a TATA box and a polyadenylation signal and was quite similar to the LTR sequence of the recently isolated human retrovirus-related sequence HuRRS-P (Kröger, B. and Horak, I. (1987) J. Virol., 61, 2071-2075). Human and simian DNAs contain 10 to 40 copies of these elements, but mouse DNA does not contain these elements.
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