Transcriptional fusion assays and the msbA2 operon. (A) GusA activities were measured for fusions in genes SMb21189, SMb21190, and msbA2 in wild-type (Rm1021) and chvI261 mutant (SmUW38) strain backgrounds. No GusA activities above background levels were detected for fusions to SMb21189 and SMb21190 in the chvI261 mutant strain background. (B) In the operon diagram, F1, F2, and F3 represent the positions of the fusions to SMb21189, SMb21190 and msbA2 respectively. The grey box (B) represents the region for ChvI binding, and P1 and P2 are predicted promoters.