Externally suppressible proline quadruplet ccc U.

Three (+1) frameshift mutations located at different genetic sites respond with high specificity to the same external suppressor. In each case, the suppressor restores small amounts of protein that is normal in electrophoretic mobility and heat stability. One of these proteins has been shown to have the wildtype amino acid sequence. The messenger RNA quadruplet CCCUappears to be common to all three frameshift sites and to be translated by the suppressor as proline. A likely suppressor agent is a proline transfer RNA with a quadruplet anticodon or its functional equivalent.