A technique for the isolation of mutants of Escherichia coli affected in degradation of cellular RNA.

Using a semiautomatic technique for handling large numbers of Escherichiacoli colonies, mutants that fail to digest their cellular RNA were isolated. This was achieved by using multiwell plates where each colony is cloned in an individual well. Cells labeled with a radioactive RNA precursor were starved for a carbon source at a high temperature. In order to assess whether or not degradation of cellular RNA took place, aliquots of each culture were subjected to autoradiography. A number of mutants defective in decay of RNA were isolated. One of them was characterized, and was found to be deficient specifically in the enzyme polynucleotide phosphorylase. Experiments carried out with this strain indicate that this enzyme participates in the degradation of "stable" RNA during carbon starvation.