Control experiments demonstrated that the LexA-UL44 protein did not activate expression of either HIS3 or lacZ reporter gene by itself and, as expected [9, 14] , could both interact with UL54 and dimerize (Table 1 and data not shown). Thus, this bait was used to screen two different cellular cDNA libraries fused to S. cerevisiae GAL4 activation domain (GAD), one derived from human B lymphocytes [48] and the other from promyelocytic HL-60 cells [49] . A total of 167 or 85 colonies, respectively, were positive for both HIS3 and lacZ reporter genes. Plasmids encoding putative interactors of UL44 were isolated from double-positive clones and retransformed into yeasts expressing LexA-UL44 in order to confirm the interaction. The 28 and 13 positive clones after this retransformation, respectively, were sequenced.