Association of a synthetic precistronic region with 70S ribosomes is enhanced by an intact initiation triplet and a sequence complementary to the 3'-terminus of 16S rRNA.

The sequence, AGGACAUAUGp, which is identical to the precistronic region of the bacteriophage Q beta A protein was synthesized by chemical and enzymatic means. Methods for synthesizing this sequence and analogues of this sequence using RNA ligase forward and back reactions from short oligonucleotides of defined sequence, are reported, including a useful means of purifying the oligonucleotides by preparative electrophoresis, as well as removal of 32p-ATP, salts and buffers by a simple filter binding technique. E. coli 70S ribosomes bind the synthetic native precistronic region substantially better than related probes in which the 16S complementary region, AGCA, is replaced by the anticomplementary region, UCCU, or is altogether absent. In addition, an intact initiation codon, AUG, is essential for interaction of mRNA with prokaryotic ribosomes.