Sigma-70 | definition of Sigma-70 by Medical dictionary
sigma factor (redirected from Sigma-70)
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a factor that inhibits the nonspecific DNA binding of RNA polymerase, as well as helping to identify the starting point of transcription; it promotes attachment of the RNA polymerase to specific initiation sites.
Synonym(s): σ factor
A protein component of bacterial RNA polymerase that recognizes the correct site on DNA for initiating transcription of a gene and that is usually released soon after transcription begins.
sigma factor a subunit of RNA polymerase that determines the site where transcription begins. The sigma factor confers PROMOTER specificity, assisting the RNA polymerase in recognising the correct promoter sequence on the DNA to initiate transcription. In ESCHERICHIA COLI the principal sigma factor is σ70, the housekeeping factor (see HOUSEKEEPING GENES).There are alternative sigma factors governing the expression of genes in response to different environmental conditions; for example σ38, the STATIONARY PHASE factor, and σ32, the heat shock factor (see HEAT SHOCK PROTEIN). These factors can associate with the RNA polymerase, displacing σ70 and directing the enzyme to initiate transcription from other promoters. see ANTISIGMA FACTOR.