Also found in: Dictionary, Encyclopedia, Wikipedia.
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
Farlex Partner Medical Dictionary © Farlex 2012
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.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.
sigma factora 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.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005