Figure 1 Transcription map of human adenovirus serotype 5. The 100 map unit (—36 kb) genome is divided into 4 early region transcription units, E1-E4, and 5 families of late mRNA, L1-L5, which are alternative splice products of a common late transcript expressed from the major late promoter located at 16 map units. Four smaller transcripts, pIX, IVa, and VA RNAs I and II, are also produced. The 103 bp inverted terminal repeats (ITRs) are located at the termini of the genome and are involved in viral DNA replication, and the packaging signal located from nucleotides 190 to 380 at the left end is involved in packaging of the genome into virion capsids.

on the cell surface (2-4), followed by a secondary interaction between the virion penton base and avp3 and avp5 integrins (5). The efficiency with which Ad binds and enters the cell is directly related to the level of primary and secondary receptors present on the cell surface (6,7). Penton-integrin interaction triggers Ad internalization by endocytosis, following which the virion escapes from the early endosome into the cytosol prior to lysosome formation (8,9). The virion is sequentially disassembled during translocation along the microtubule network toward the nucleus where the viral DNA is released into the nucleus (10). Once in the nucleus, viral DNA replication, beginning 6-8 h postinfection, and assembly of progeny virions occur. The entire life cycle takes about 24-36 h, generating about 104 virions per infected cell. Ads have never been implicated as a cause of malignant disease in their natural host and, in immunocompetent humans, most infections caused by the most common serotypes are relatively mild and self-limiting. For a more comprehensive discussion of adenoviruses, the reader is referred to the excellent review by Shenk (1).

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