RaSH, a rapid subtraction hybridization approach for identifying and cloning differentially expressed genes.

Human melanoma cells growth-arrest irreversibly and terminally differentiate on treatment with a combination of fibroblast interferon and the protein kinase C activator mezerein. This experimental protocol also results in a loss of tumorigenic potential and profound changes in gene expression. Various cloning and cDNA microarray strategies are being used to determine the complete spectrum of gene expression changes underlying these alterations in human melanoma cells. An efficient approach, Rapid Subtraction Hybridization (RaSH), has been developed that is permitting the identification of genes of potential relevance to cancer growth control and terminal cell differentiation. RaSH cDNA libraries are prepared from double-stranded cDNAs that are enzymatically digested into small fragments, ligated to adapters, and PCR amplified followed by incubation of tester and driver PCR fragments. This subtraction hybridization scheme is technically simple and results in the identification of a high proportion of differentially expressed sequences, including known genes and those not described in current DNA databases. The RaSH approach represents an efficient methodology for identifying and cloning genes displaying differential expression that associate with and potentially regulate complex biological processes.