The diribonucleoside monophosphate CpA (and no others) inhibits polypeptide chain elongation in rabbit reticulocyte lysates at 10–50 μM. Furthermore, all the trinucleotides containing CpA, i.e., XpCpA and CpApX (X = U, C, A or G) block polypeptide chain elongation as well. At 10 μM the inhibition by XpCpA and not CpApX is transient because a 3'-exonucleolytic activity destroys the critical CpA moiety. The inhibitors do not appear to interfere with the aminoacylation of tRNAs or disrupt the interaction of aminoacyl-tRNAs with the protein synthetic machinery. High levels (200 μM) of CpA or the trinucleotides containing CpA have no effect on translation in a wheat germ cell-free system.
