Direction of reading of the genetic message. II.

Abstract

Synthetic oligonucleotides of the type ApApAp ApApCpAp...pApApA (A5CAn) and ApApApApCpAp... pApApA (A4 CAn) have an ApApA triplet at the 5[image] -end, followed by the asparagine codon pApApC in the A5CAn series, or by the threonine codon pApCpA in the A4CAn series. These are followed in both series by a number of pApApA (lysine) codons. In a system of purified E. coli ribosomes and L. arabinosus supernatant, of low nuclease content, A5CAn oligonucleotides directed mainly the synthesis of lysine oligopeptides with NH2-terminal asparagine, whereas A4CAn polymers directed predominantly the synthesis of lysine oligopeptides with NH2-terminal threonine. The initial ApApA triplet in these polymers was thus infrequently read. Together with earlier work these results provide conclusive evidence for the 5[image] [forward arrow] 3[image] polarity of messenger translation. They also show that the above oligonucleotides are not read randomly by the cellfree system.