Table 1

Regulation of expression and ribosome-binding activity of variant btuB RNAs

RNA sequence*β-Galactosidase activityPrimer extension products, %
TRX fusion TRL fusion T256 A202
lac 86.285.3 (1.0)
btuB wild type2,200340 (6.5)405332.514.1 (2.3)4.621.0
 Δ(B12 box)10090 (1.1)3410.79.9 (1.1)<2<2
 M262,7002400 (1.1)59043075.974.3 (1.0)2.411.6
 M272,8702470 (1.1)72056058.731.9 (1.8)2.916.9
 M26.271,610315 (5.1)2201753.825.8 (2.1)2.814.6
 M31530280 (1.9)26516.311.5 (1.4)1.51.5
 M35390310 (1.3)22313.513.3 (1.0)1.51.7
 M31.351,600550 (2.9)95128.411.8 (2.4)2.110.3
 M36330390 (0.8)136NDND
 M31.36650420 (1.5)1512NDND
  • * The sequence changes in the variant btuB leader regions are presented in Fig. 4

  • β-Galactosidase activity was measured in cells carrying the variant btuB leader sequences present in btuB-lacZ transcriptional fusions expressed in plasmid pRS415 (TRX fusion) or in btuB-lacZ translational fusions expressed in plasmid pRS414 (TRL fusion). The insert in both plasmids carried the btuB sequences from positions −60 to +450. Cells were grown in the absence and presence of 5 μM Ado-Cbl, as indicated, and the repression ratio (−Ado-Cbl/+Ado-Cbl) is shown in parentheses for the transcriptional fusions. 

  • The levels of the T256 and A202 products are presented as a percentage of the amounts of the major primer extension products. The results are average values of three experiments, one shown in Fig. 5. The value −Ado-Cbl/value +Ado-Cbl is shown in parentheses for the T256 ribosome-binding assay.