Unique genes contributed by individual cell lines to URRR. RNA from 14 individual rat cell lines were reverse-transcribed to cDNA, labeled with Cy5 and co-hybridized with Cy3-labeled URRR onto 14,000-spot rat cDNA microarrays (Agilent). The data was analyzed using GeneTraffic software. 400–1200 spots out of 14,000 were flagged on each microarray and excluded from further analysis. Spots with hybridization signals in Cy5 channel higher than 1000 and with Cy5/Cy3 ratio greater than 2 were collected and the number of spots with these characteristics on only one microarray was determined.