TERMINATION OF TRANSLATION IN BACTERIA MAY BE MODULATED VIA SPECIFIC INTERACTION BETWEEN PEPTIDE-CHAIN RELEASE FACTOR-II AND THE LAST PEPTIDYL-TRANSFER RNA(SER PHE)/

The 5' context of 671 Escherichia coli stop codons UGA and UAA has bee n compared with the context of stop-like codons (UAC, UAU and CAA for UAA; UGG, UGC, UGU and CGA for UGA). We have observed highly significa nt deviations from the expected nucleotide distribution: adenine is ov er-represented whereas pyrimidines are under-represented in position - 2 upstream from UAA. Uridine is over-represented in position - 3 upst ream from UGA. Lysine codons are preferable immediately prior to UAA. A complete set of codons for serine and the phenylalanine UUC codon ar e preferable immediately 5' to UGA. This non-random codon distribution before stop codons could be considered as a molecular device for modu lation of translation termination. We have found that certain fragment of E.coli release factor 2 (RF2) (amino acids 93 - 114) is similar to the amino acid sequences of seryl-tRNA synthetase (positions 10 - 19 and 80 - 93) and of beta (small) subunit (positions 72-94) of phenylal anyl-tRNA synthetase from E. coli. Three-dimensional structure of E.co li seryl-tRNA synthetase is known [1]: its N-terminus represents an an tiparallel alpha-helical coiled-coil domain and contains a region homo logous to RF2. On the basis of the above-mentioned results we assume t hat a specific interaction between RF2 and the last peptidyl-tRNA(Ser/ Phe) occurs during polypeptide chain termination in prokaryotic riboso mes.