SELECTION OF CDNAS FOR PHOSPHODIESTERASES THAT HYDROLYZE GUANOSINE 3'5'-MONOPHOSPHATE IN ESCHERICHIA-COLI

A genetic selection procedure has been developed which makes the growt h of E. coli dependent on expression of a cGMP phosphodiesterase cDNA. E. coli does not contain a cGMP phosphodiesterase, and guanine auxotr ophs cannot extract the guanine from cGMP. If a functional cGMP phosph odiesterase is introduced, then guaA auxotrophs will grow on cGMP as a guanine source. The method also selects GMP synthetase cDNAs, which c omplement the guanine auxotrophy directly. Expression of a Dictyosteli um discoideum or human heart cyclic nucleotide phosphodiesterase cDNA permits growth of the E. coli guaA auxotroph in the presence of cGMP. Several commercial cDNA libraries were corrupt and contained phosphodi esterase and/or GMP synthetase sequences that were from a contaminatin g DNA source.