Avian endogenous retrovirus EAV-HP shares regions of identity with avian leukosis virus subgroup j and the avian retrotransposon ART-CH

The existence of novel endogenous retrovirus elements in the chicken genome , designated EAV-HP, with close sequence identity to the env gene of avian leukosis virus (ALV) subgroup J has been reported (L.M. Smith, it A. Toye, ii. Howes, TV. Bumstead, L. N. Payne, and K. Venugopal, J, Gen, Virol. 80:2 61-268, 1999). To resolve the genome structure of these retroviral elements , we have determined the complete sequence of two proviral clones of EAV-HP from a Line N chicken genomic DNA yeast artificial chromosome library and from a meat-type chicken line 21 lambda library, The EAV-HP sequences from the two lines were 98% identical and had a typical provirus structure. The two EAV-HP clones showed identical large deletions spanning part of the gag , the entire pol, and part of the air genes. The env region of the EAV-HP c lones was 97% identical to the env sequence of HPRS-103, the prototype subg roup J ALV. The 5' region of EAV-HP comprising the R and U5 regions of the long terminal repeat (LTR), the untranslated leader, and the 5' end of the putative Sag region were 97% identical to the avian retrotransposon sequenc e? ART-CH. The remaining gag sequence! shared less than 60% identity with o ther ALV sequences. The U3 region of the LTR was distinct from those of oth er retroviruses but contained some of the conserved motifs required for fun ctioning as a promoter. To examine the ability of this endogenous retrovira l LTR to function as a transcriptional promoter, the EAV-HP and HPRS-103 LT R U3 regions R ere compared in a luciferase reporter gene assay. The low lu ciferase activity detected with the EAV-HP LTR U3 constructs. at levels clo se to those observed for a central vector lacking the promoter or enhancer elements, suggested that these elements function as a weak promoter, possib ly accounting for their low expression levels in chicken embryos.