Similarity and divergence between the RNA polymerase α subunits from hyperthermophilic Thermotoga maritima and mesophilic Escherichia coli bacteria

The α subunit (αTm) of Thermotoga maritima RNA polymerase has been characterized to investigate its role in transcriptional regulation in one of the few known anaerobic hyperthermophilic bacteria. The highly thermostable αTm shares 54% similarity with its Escherichia coli analogue (αEc). The T. maritima rpoA gene coding the α subunit does not complement the thermosensitive rpoA112 mutation of E. coli. However, αTm and αEc show similar folding patterns as determined by circular dichroism. Purified αTm binds to the T. maritima PargGo promoter region (probably to a UP-element) and Arg282 appears to be crucial for DNA binding. The thermostable protein is also able to interact with transcription regulatory proteins, like ArgR from T. neapolitana or CRP from E. coli. These data indicate that the RNA polymerase α subunit might play a crucial role in the modulation of gene expression in hyperthermophiles.