Expression profiles of 20 human tRNA synthetases in 18 tissues. Rows and columns of the matrix represent genes and tissues, respectively. Tissues are ranked from the poorly-sampled (left) to the highly-sampled (right) according to the EST data. The darkness of the blue color indicates the original EST counts in EST data (A) and expression intensities in microarray data (B). Blank squares indicate absence of detection. Original EST counts are kept to demonstrate the increasing capability of gene identification from poorly-sampled to highly-sampled tissues.