Abstract
Polypeptide release factor 2 (RF2) in Escherichia coli is known to be synthesized by a +1 frameshift at the 26th UGA codon of RF2 mRNA. Polyamines were found to stimulate the +1 frameshift of RF2 synthesis, an effect that was reduced by excess RF2. Polyamine stimulation of +1 frameshift of RF2 synthesis was observed at the early logarithmic phase, which is the important phase in determination of the overall rate of cell growth. A Shine-Dalgarno-like sequence was necessary for an efficient +1 frameshift of RF2 synthesis, but not for polyamine stimulation. Spectinomycin, tetracycline, streptomycin, and neomycin reduced polyamine stimulation of the +1 frameshift of RF2 synthesis. The results suggest that a structural change of the A site on 30 S ribosomal subunits is important for polyamine stimulation of the +1 frameshift. The level of mRNAs of ribosomal proteins and elongation factors having UAA as termination codon was enhanced by polyamines, and OppA synthesis from OppA mRNA having UAA as termination codon was more enhanced by polyamines than that from OppA mRNA having a UGA termination codon. Furthermore, synthesis of ribosomal protein L20 and elongation factor G from the mRNAs having a UAA termination codon was enhanced by polyamines at the level of translation and transcription. The results suggest that some protein synthesis from mRNAs having a UAA termination codon is enhanced at the level of translation through polyamine stimulation of +1 frameshift of RF2 synthesis. It is concluded that prfB encoding RF2 is a new member of the polyamine modulon.
Highlights
Polyamines, aliphatic cations present in almost all living organisms, are necessary for normal cell growth [1,2,3]
Effect of Polyamines on in Vivo ϩ1 Frameshift of release factor 2 (RF2) Synthesis—It is well known that AZ synthesis involves a ϩ1 frameshift at the 69th termination codon of open reading frame (ORF) of AZ mRNA in mammalian cells, and the efficiency of this frameshift is enhanced by polyamines [21, 22]
Because RF2 in E. coli is synthesized by a ϩ1 frameshift at the 26th termination codon (Fig. 1A) [27, 28], the effect of polyamines on the efficiency of this frameshift was examined using the polyamine-requiring mutants MA261 and DR112
Summary
Polyamines (putrescine, spermidine, and spermine), aliphatic cations present in almost all living organisms, are necessary for normal cell growth [1,2,3]. Synthesis of ribosomal protein L20 and elongation factor G from the mRNAs having a UAA termination codon was enhanced by polyamines at the level of translation and transcription.
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