Defective variants of adenovirus type 3 (Ad3) have been isolated from a heterogeneous, high multiplicity passage stock of the virus. A strikingly defective variant, Ad3hr15, fails to propagate on normally permissive A549 cells, yet has greater infectivity than wild type Ad3 in the adenovirus type 5 (Ad5) DNA-transformed 293 cell line. Investigation of its genomic alterations revealed that Ad3hr15 bears two short tandem duplications of viral DNA sequences near its left end, 5′ to the ElA gene. The variant also bears a large tandem triplication at its right end. Marker rescue experiments with plasmid-cloned left end DNA sequences of Ad3 implicate that the duplications 5′ to ElA are responsible for the Ad3hr15 defect and the ElA structural gene of the variant is functional. Northern analysis revealed no detectable ElA transcripts early after Ad3hr15 infection of A549 cells. The 293 cell line, however, supports high levels of transcription of the Ad3 ElA gene by the mutant Ad3hr15 ElA promoter.
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