Development of β-Lactamase as a Tool for Monitoring Conditional Gene Expression by a Tetracycline-Riboswitch in Methanosarcina acetivorans

Table 2

tc-dependent Bla activity in M. acetivorans strains carrying mcrB_P-tc-RS-blaN gene fusions.

tc-RS construct	Bla activity^a		-fold regulation^b	P1 length; (bp)	RBS bases in P1	P1 stability; Δ𝐺 (kcal mol^−1)^c
	−tc	+tc
𝑚𝑐𝑟𝐵𝑃	36±6	39±4	—	—	—	—
tc-RS1	104±2	40±2	2.6	7	1	−5.6
tc-RS2	71±2	40±3	1.8	7	2	−5.6
tc-RS3	43±5	16±2	2.7	7	3	−5.1
tc-RS4	340±10	29±9	11.6	7	4	−4.4
tc-RS4a	21±2	8±1	2.6	8	4	−7.7
tc-RS4b	14±2	7±1	2.0	8	4	−7.7
tc-RS5	1.5±0.4	n.d.	—	7	6	−7.1

aValues are given in mU (nmol min⁻¹) mg⁻¹ and are averages of three independent cultures grown in the absence (−) or presence (+) of 200 𝜇M tc; ± denotes the standard deviation; all experiments were reproduced at least once.
^bValues (−tc/+tc) were corrected by substracting those of the negative control (-prom).
n.d.: below detection limit of the assay.
^cStability was calculated using mfold (http://mfold.rna.albany.edu/).