ABSTRACT
The effect on the translation efficiency of various mutations in the three bases (the -1 triplet) that precede the AUG start codon of the beta-galactosidase mRNA in Escherichia coli was studied. Of the 39 mutants examined, the level of expression varies over a 20-fold range. The most favorable combinations of bases in the -1 triplet are UAU and CUU. The expression levels in the mutants with UUC, UCA or AGG as the -1 triplet are 20-fold lower than those with UAU or CUU. In general, a U residue immediately preceding the start codon is more favorable for expression than any other base; furthermore, an A residue at the -2 position enhances the translation efficiency in most instances. In both cases, however, the degree of enhancement depends on its context, i.e. the neighboring bases. Although the rules derived from this study are complex, the results show that mutations in any of the three bases preceding the start codon can strongly affect the translational efficiency of the beta-galactosidase mRNA.
Subject(s)
Galactosidases/genetics , Protein Biosynthesis , beta-Galactosidase/genetics , Base Sequence , Binding Sites , Codon , Escherichia coli/genetics , Mutation , Nucleic Acid Conformation , Operon , Peptide Chain Initiation, Translational , Ribosomes/metabolism , Structure-Activity RelationshipABSTRACT
The conformation of d(TA)3 (CG)3 has been studied in aqueous solution in the presence of high salt concentration. The oligonucleotide forms in solution concatamers. In the presence of 5 M NaC1 the concatamer is built up of d(CG)3 blocks in Z-conformation and of d(TA)3 blocks in B-conformation. In the presence of 4 M LiCl both blocks in the concatamer display a B-type structure.
Subject(s)
Nucleic Acid Conformation , Oligodeoxyribonucleotides , Oligonucleotides , Circular Dichroism , Drug Stability , Osmolar Concentration , Structure-Activity RelationshipABSTRACT
The conformation of d (CG)n oligomers with n = 2,3 has been studied in aqueous solution in the presence of high salt concentration. A minimum n value of three is necessary to obtain a left-handed Z-helix. When d (CG)3 is flanked by three non Z-helicogenic alternating AT sequences the left-handed helix is unstable and a B-type conformation is obtained also at high salt concentration.
