Manipulation of Early Region 4
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Early region 4 (E4; Fig. 1A ) occupies the right-hand 3000 bp of the human adenovirus genome. The sequences of E4 and E4 cDNAs indicate that E4 encodes seven polypeptides (
1
–
4
), most of which have been detected in infected cells. Analysis of E4 mutants has implicated E4 products in a variety of processes that occur in infected cells, including viral early and late gene expression, DNA replication, the shutoff of host-cell protein synthesis, transformation, and the ability to stimulate replication of adenovirus-associated virus (AAV). Specific E4 products have been implicated in many of those processes and, in some cases, information on the molecular mechanisms of E4 function is emerging. Current knowledge of the functions of E4 products is summarized below.
Fig. 1
A
) The organization of adenovirus early region 4 E4 open reading frames (ORFs) are indicated by open boxes above a scale that indicates position in map units (0 to 100; 1 map unit is approx 360 bp) and nucleotide numbers. ORFs 1,2,3,4, and 6 are colinear with the viral DNA; ORFs 3/4 and 6/7 are the result of inframe splicing of the E4 mRNA precursor E4 is transcribed from right to left. (
B
) Reconstruction of an intact viral genome by ligation in vitro (
C
) Reconstruction of an intact viral genome by overlap recombination. (
D
) Construction of an E4 mutant by recombination between a plasmid and an E4 deletion mutant In C and D, the X indicates a potential homologous recombination event. In B, C, and D, the position of a hypothetical E4 mutation is noted by a V
