Further Codon Assignments in an Extremely Halophilic Bacterium using a Cell-Free Protein-Synthesizing System and a Ribosomal Binding Assay

Further codon assignments were made in a cell-free protein-synthesizing system from Halobacterium cutirubrum by use of the random copolyribonucleotides, poly CU, poly CI, poly CG, and poly AU. Polymers containing significant amounts of adenosine precipitated in the high salt concentration of the system and this prevented examination of many of the codons by this technique. An assay for codon recognition and interaction of aminoacyl-tRNA with ribosomes was developed in order to utilize oligoribonucleotides which had a high proportion of adenosine but which would not precipitate in the high salt systems. The codon AAA was assigned to lysine on the basis of this technique. It was found that glutaminyl-tRNA Gln was made via the intermediate glutamyl-tRNA Gln as it is in Gram-positive bacteria.