Determination of DNA hybridization sensitivity by titration. Genomic DNA of infected cells was isolated and HHV-6 viral copy number was determined by a TaqMan assay , as described in Materials and Methods. The DNA was then serially diluted (3 μg, 1 μg, 0.3 μg, 0.01 μg), labeled, and hybridized to the array. Hybridizations that resulted in a ratio of less than 2 were considered as non-hybridization and are indicated in blue. Hybridizations that resulted in a ratio of two to ten were considered low hybridization intensities and are indicated in yellow, while high hybridizations resulting in a ratio greater than ten are indicated in red.