Codon assignments and fidelity of translation in a cell-free protein-synthesizing system from an extremely halophilic bacterium.

Abstract

The incorporation of 14C-labelled amino acids into material insoluble in hot TCA under the direction of synthetic polyribonucleotides has been studied in a preincubated, cell-free system from Halobacterium cutirubrum. In the presence of 3.8 M KCl and 1.1 M NH4 salts, polyuridylic acid directed the incorporation of phenylalanine and also of leucine to the extent of 8% miscoding. This miscoding for leucine was reduced to 1% in the presence of 3.8 M KCl, 1.0 M NaCl, and 0.4 M NH4Cl. Poly C directed the incorporation of proline. The random heteropolyribonucleotides poly CA, poly CU, and poly UG directed the incorporation of only those amino acids expected on the basis of the established genetic code, together with methionine with poly UG. Quantitative comparison of the incorporation with the calculated frequencies of triplets in these polyribonucleotides suggests that the codon assignments investigated in H. cutirubrum could be identical with those in non-halophilic organisms.