A HYPERVARIABLE REGION IN VP1 OF CHICKEN INFECTIOUS-ANEMIA VIRUS MEDIATES RATE OF SPREAD AND CELL TROPISM IN TISSUE-CULTURE

Chicken infectious anemia virus (CIAV) is a unique infectious agent wi th an amino acid composition that has been found to be remarkably cons erved even in isolates from different parts of the world, We have char acterized field isolates of CIAV which vary significantly in terms of their abilities to replicate in culture, demonstrating a biological di fference between isolates, Two sublines of MDCC-MSB1 cells that differ in their abilities to support CIAV mere identified. In the MSB1(S) su bline the CIA-1 isolate of CIAV was found to be less cytopathogenic th an the prototype Cux-1(C) isolate; the MSB1(L) subline, which supports Cux-1(C) replication, was found to be nonpermissive for CIA-1. Alignm ents of the VP1 sequences of previously examined isolates with those o f the field isolates CIA-I and L-028 and the culture-adapted ConnB iso late revealed a previously unreported hypervariable region spanning am ino acid positions 139 to 151. Chimeras of Cux-1 (C) and CIA-1 mere co nstructed to examine the potential for this region to affect cytopatho genicity, Transfer of a 316-bp region of Cus-1(C) open reading frame 1 into CIA-1 produced a virus with a cytopathogenic profile typical of Cux-1(C), indicating that one or both of the amino acid differences at positions 139 and 144 affect the rate of replication or the spread of infection. Transfection experiments with additional chimeras indicate d that the inability of CIA-1 to replicate in MSB1(L) cells is mediate d by a larger region of the genome which contains the hypervariable re gion in addition to upstream amino acid differences, Analysis of chime ras excluding the entire region of open reading frame 1 suggested the presence of a secondary mediator in the progression of infection in cu lture that R as localized to a region containing a single nucleotide d ifference which results in amino acid differences in both VP2 (V-153) and the nuclear localization signal of VP3 (C-118). Immunofluorescence assays indicated an increased cytoplasmic distribution of VP3 and a g eneral lack of VP3-associated apoptatic bodies in infections of CIA-1 and chimeras containing V-153 or C-118, as opposed to a primarily nucl ear distribution and association with well-formed apoptotic bodies in Cux-1(C)-infected cells.