Characterization of 39 independent isolated mutants with increased frameshifting activity caused by increased geranylation activity following localized mutagenesis of the mnmH gene or by whole genome selection for increased frameshifting activity.

A. Mutants were isolated following localized mutagenesis as described in M-M. All alterations in MnmH were obtained by the mutagen hydroxylamine except the alterations A63P and one of the two L66P alterations which were obtained using overexpression of dinB and the mutagen nitrosoguanine, respectively. In addition three mutants (One G67E and two G67R) obtained by Riddle and Roth [6] and one mutant (G67R) obtained by Jäger et al [7] are also included in the table. All these mutants have increased +1 frameshifting activity (data not shown), which is a caused by increased geranylation of tRNA. We did not observe a simple correlation between ability to suppress a +1 frameshift mutation to the level of cmnm5ges2UpU, which might not be expect, since induction of frameshifting is complex although partly dependent on a decreased level of charged Gln- [4]. B. Total ges2-derivatives consist of the level of cmnm5ges2U and mnm5ges2U determined as described in S1 Fig. Standard deviations are given as +/-. C. Not done. The level of the geranylation in these double mutants was not determined since they all had an alteration, which as a single alteration give increased geranylation activity. They all had increased frameshifting activity. D. Values are from Table 1. E. Following independent isolated mutants with G67R alteration in MnmH are present in strains GT945 and GT946 [6]. In addition, but not included in this table, are strains GT8190 (G67R) and GT8194 (G67V), which were obtained by scrambling the codon in position 67 (Table 1).