Abstract
In cell-free protein synthesis studies with RNA from phage MS2 as template, normal Escherichia coli tRNASer3 promotes two base translocation at GCA alanine codons with a resultant shift of ribosomes to the minus one reading frame. Similarly, normal tRNAThr3 promotes two base translocation at CCG proline codons. These conclusions were reached by amino acid sequencing of tryptic peptides or cyanogen bromide fragments that contained the reading frame shift site. It is proposed that these frameshift events occur by a two-base pair interaction between the anticodons of these exceptional tRNAs and the noncognate codons.
Highlights
When a ribosome shifts reading frame, it will synthesize a amino acid sequencing of tryptic peptides or cyanogehnybrid protein until it encounters the first terminator in the bromide fragments that contained the reading frame shift site
It has recently become apparent thatsome proteins can be all proline or alanine codons, and as shown in Fig. 2, there synthesized only if a specific ribosomal frameshift event oc- are many such codons in the window that could give rise to curs allowing decoding of adjacent sequences of their mRNAs proteins 6 and 7
The most convincing exam- these events would have an amino acid sequence different ples include the product of gene 10 of the DNA bacteriophage from the others at a few internal positions
Summary
In cell-free protein synthesis studies with RNA from 7. This effect is ameliorated by tRNAAlal, whichdecodes phage MS2 as templaten, ormal Escherichia coli GCU/GCA/GCG [17], as if the serine tRNAis reading alanine tRNASerspromotes two basetranslocationat GCA codons to give a minus one shift. ACU/ACC decodalanine codons with a resultant shift of ribosomes to ing tRNAThrs [18, 19] appears to cause minus one framethme inuosnreeadingframe. Normal shifting at proline codons in both the coat protein and syntRNAThrBpromotes two basetranslocation at CCG thetase genes of MS2 [13]. The resultant protein will be shorter or longer than the normal product depending upon the location of the firstdownstream terminator in thenew reading frame. For proteins 6 and 7, the “window”available for frameshifting is delimited by the zero frame terminator and by the first upstream terminator in theminus one frame
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