DIRECT CHEMICAL METHOD FOR SEQUENCING RNA

Four different base-specific chemical reactions generate a means of directly sequencing RNA terminally labeled with 32P. After a partial, specific modification of each kind of RNA base, an amine-catalyzed strand scission generates labeled fragments whose lengths determine the position of each nucleotide in the sequence. Dimethyl sulfate modifies guanosine. Diethyl pyrocarbonate attacks primarily adenosine. Hydrazine attacks uridine and cytidine, but salt suppresses the reaction with uridine. In all cases, aniline induces a subsequent strand scission. The electrophoretic fractionation of the labeled fragments on a polyacrylamide gel, followed by autoradiography, determines the RNA sequence. RNA labeled at the 3' end yields clean cleavage patterns for each purine and pyrimidine and allows a determination of the entire RNA sequence out to 100-200 bases from the labeled terminus.