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Characterization of IS 1221 from Mycoplasma hyorhinis : expression of its putative transposase in Escherichia coli incorporates a ribosomal frameshift mechanism
Author(s) -
Zheng Jianhong,
McIntosh Mark A.
Publication year - 1995
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.1995.tb02429.x
Subject(s) - biology , translational frameshift , frameshift mutation , open reading frame , transposase , genetics , insertion sequence , inverted repeat , ribosomal binding site , stop codon , transposable element , ankyrin repeat , eukaryotic translation , start codon , upstream open reading frame , direct repeat , translation (biology) , gene , peptide sequence , messenger rna , mutation , mutant , genome , base sequence
Summary Seven complete and two partial copies of IS 1221 variants from Mycoplasma hyorhinis and Mycoplasma hyopneumoniae characterized to date have established a consensus IS 1221 as a 1513 bp element with unique structural characteristics resembling the IS 3 family of bacterial insertion sequences. Each IS 1221 copy contains highly conserved 28 bp imperfect terminal inverted repeats and three distinctive internal inverted repeats (LIR, RIR and IIR). IIR is located within the coding region of the element and it is proposed that it plays a critical role in the regulation of putative transposase expression. Consensus IS 1221 and one particular copy, G1135.2, contain a single long open reading frame (ORF). Two potential initiation codons are present at nucleotide 46 (AUG46) and nucleotide 397 (AUG397) and both are preceded by strong ribosome‐binding sites. Both initiation codons can be used efficiently in an Escherichia coli T7 expression system. The LIR has a negative regulatory effect on translation initiation from AUG46. A ‐1 translational frameshift event is shown to be involved in expression of the IS 1221 ORF and results in the production of 20kDa and 6kDa truncated proteins from the respective upstream initiation codons of the IS 1221 ORF. Base substitution and deletion mutations in sequences resembling characterized motifs in documented examples of translational frameshifting resulted in a significant increase in the full‐length products and a corresponding decrease in the truncated products from the IS 1221 ORF. In contrast to the usual ‐1 frameshift regulatory event in the IS 3 family, which produces a transframe fusion product as the active transposase, IS 1221 may have evolved a high‐frequency ‐1 frameshift mechanism that produces a truncated product from the upstream coding domain and thereby results in the regulated low‐level production of the full‐length presumptive transposase.