AUTHOR=Ding Yan , Berezuk Alison , Khursigara Cezar M. , Jarrell Ken F. 

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

JOURNAL=Frontiers in Microbiology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2017.01329

DOI=10.3389/fmicb.2017.01329

ISSN=1664-302X

ABSTRACT=<p>In <italic>Methanococcus maripaludis</italic>, the euryarchaeal archaellum regulator A (EarA) is required for the transcription of the <italic>fla</italic> 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 <italic>earA</italic> (Δ<italic>earA</italic>), there is almost undetectable transcription of the <italic>fla</italic> operon, Fla proteins are not synthesized and the cells are non-archaellated. In this study, we have isolated a spontaneous mutant of a Δ<italic>earA</italic> mutant in which the restoration of the transcription and translation of the <italic>fla</italic> operon (using <italic>flaB2</italic>, 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 <italic>fla</italic> 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<italic>earA</italic> mutant, very similar phenotypes to that of the spontaneous mutant were observed. Deletion of the three adenines in the <italic>fla</italic> promoter BRE resulted in the mutant BRE having high sequence identity to BREs from promoters that have strong basal transcription level in <italic>Mc. maripaludis</italic> and <italic>Methanocaldococcus jannaschii</italic>. These data suggest that EarA may help recruit transcription factor B to a weak BRE in the <italic>fla</italic> promoter of wild-type cells but is not required for transcription from the <italic>fla</italic> promoter with a strong BRE, as in the three adenine deletion version in the spontaneous mutant.</p>