Table 2.

Effect of arabinose concentration on the viability of E. coli BW27784 expressing different recombinant YTOP proteins under the control of the BAD promoter

Arabinose concentration (%)	R.V. pAYTOP	R.V. pAYTOP128	R.V. pAYTOP-G122S	R.V. pAYTOP-G122S/M326V
0	1	1	1	1
0.00006	0.84 ± 0.09	0.014 ± 0.005	0.065 ± 0.007	0.016 ± 0.007
0.0002	0.48 ± 0.16	0.0014 ± 0.0002	0.020 ± 0.003	0.0012 ± 0.0009
0.002	0.25 ± 0.11	0.00035 ± 0.00008	0.0091 ± 0.0006	0.00023 ± 0.00014

Relative viability was determined by calculating the ratio of the viable colony counts after 2 h of induction with the indicated arabinose concentration versus the viable colony counts from the non-induced culture. The recombinant YTOP proteins were expressed in low copy number plasmids (pAYTOP and its derivatives). The results shown represent the average and standard deviation of at least four different measurements for the mutant YTOP proteins and three different measurements for wild-type YTOP. Mutant pAYTOP128 had a third A383P substitution in addition to G122S and M326V mutations. Single mutation of A383P or M326V in YTOP did not induce SOS response when induced by arabinose and had no significant effect on viability (12).