Transcription in the Archaea: Basal factors, regulation, and stress-gene expression

A brief survey is presented of salient findings on transcription in the Archaea, focussing on stress genes of the hsp70(dnaK locus, which code for the molecular chaperones Hsp70(DnaK), Hsp40(DnaJ), and GrpE. Archaeal basal factors and some recently characterized regulators pertinent to non-stress genes are presented first to show their similarities and differences with equivalents in organisms of the other two phylogenetic domains, Bacteria and Eucarya, and to reveal clues on how these or similar factors might transcribe and regulate the archaeal stress genes. The second part of the article deals with the hsp70(dnaK)-locus genes, particularly those from Methanosarcina mazeii, because they are virtually the only ones within the methanogenic Archaea whose patterns of constitutive and stress-induced expressions have been studied. Therefore, these genes provide a standardized model system to elucidate transcription initiation and regulation at the molecular level in this phylogenetic group. Promoters, and other cis-acting sites that are, or might be, involved in stress-gene expression are described. Conformational changes of basal transcription factors after interaction with stress-gene promoters are discussed that suggest ways for generating a large diversity of initiation complexes using a few factors and DNA sites in different combinations. Likewise, the effects of stress on DNA topology and on TBP-TFB-promoter complex formation and tightness are described, which might also contribute to the generation of transcription-initiation complex diversity. This diversity would be key to differential gene expression, namely, which genes are transcribed, when (basal, steady expression vs. sporadic stress-induced expression), and to what level. Future research should investigate this diversity, and the mechanism of complex formation and action at the atomic, molecular, and supramolecular levels, to elucidate the dynamics of transcription initiation in real time.