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In  Methanococcus maripaludis , the euryarchaeal archaellum regulator A (EarA) is required for the transcription of the  fla  operon, which is comprised of a series of genes which encode most of the proteins needed for the formation of the archaeal swimming organelle, the archaellum. In mutants deleted for  earA  (Δ earA ), there is almost undetectable transcription of the  fla  operon, Fla proteins are not synthesized and the cells are non-archaellated. In this study, we have isolated a spontaneous mutant of a Δ earA  mutant in which the restoration of the transcription and translation of the  fla  operon (using  flaB2 , the second gene of the operon, as a reporter), archaella formation and swarming motility were all restored even in the absence of EarA. Analysis of the DNA sequence from the  fla  promoter of this spontaneous mutant revealed a deletion of three adenines within a string of seven adenines in the transcription factor B recognition element (BRE). When the three adenine deletion in the BRE was regenerated in a stock culture of the Δ earA  mutant, very similar phenotypes to that of the spontaneous mutant were observed. Deletion of the three adenines in the  fla  promoter BRE resulted in the mutant BRE having high sequence identity to BREs from promoters that have strong basal transcription level in  Mc. maripaludis  and  Methanocaldococcus jannaschii . These data suggest that EarA may help recruit transcription factor B to a weak BRE in the  fla  promoter of wild-type cells but is not required for transcription from the  fla  promoter with a strong BRE, as in the three adenine deletion version in the spontaneous mutant.

frontiers in microbiology

Bypassing the Need for the Transcriptional Activator EarA through a Spontaneous Deletion in the BRE Portion of the fla Operon Promoter in Methanococcus maripaludis