Proteins of viral and cellular origin bind to the Aleutian disease virus (ADV) DNA 3'-terminal hairpin: presentation of a scheme for encapsidation of ADV DNA.

We have observed the binding of viral and cellular proteins to the Aleutian disease virus (ADV) 3' terminus of replicative-form DNA. Gel retardation assays showed specific band shifts produced by whole-cell extracts from either ADV-infected or uninfected cells, as well as band reduction produced by ADV capsids. In all cases, binding was confined to the turnaround, T-shaped terminal form; no binding to the extended conformation of replicative-form DNA was detected. This indicates the importance of the T-shaped secondary structure in protein recognition. We have previously reported the binding of a 3'-terminal ADV DNA restriction fragment to the ADV capsid protein VP1 (K. Willwand and O.-R. Kaaden, Virology 166:52-57, 1988). Here we show that the region between nucleotides 14 and 102 on the ADV genome is required for binding. It is suggested that the VP1-DNA interaction mediates the binding of ADV DNA to empty viral capsids and that this is followed by displacement synthesis and packaging of ADV progeny DNA. A scheme for the possible mechanism of this process is presented.