E. coli produces a family of proteins called sigma () factors. a. What is the fu
ID: 208384 • Letter: E
Question
E. coli produces a family of proteins called sigma () factors.
a. What is the function of a sigma factor?
b. One of these, 70, is called the “housekeeping” sigma factor. What do you think “housekeeping” means?
c. Other sigma factors in E. coli include a general starvation (38), nitrogen starvation (54), and an excessive heat (32) sigma factor. Of what benefit is having multiple sigma factors to E. coli?
d. Sigma factor is a good example of a transcription factor. Provide five other examples (prokaryotic or eukaryotic) of transcription factors.
Explanation / Answer
a. The function of a Sigma factor ( factor) is to enable specific binding of RNA polymerase to gene promoters. The specific sigma factor used to initiate transcription of a given gene will vary, depending on the gene and on the environmental signals needed to initiate transcription of that gene.
b. E.Coli possesses 7 distinct factor - 70, 19,, 24, 28, 32, 38, 54. The Primary factor, 70, allows RNAP to recognize and bind the vast majority of promoters. Produced constitutively, 70 drives transcription of genes dedicated to everyday cellular processes. Thus 70 is called the “housekeeping” sigma factor.
c. Most Bacteria possess multiple factor variants because the competition between these factors dictates differential RNAP distribution. Accumulation of these alternative factors drives competition with 70 for the core enzyme (E). Each resultant holoenzyme (E ) can initiate transcription only from the subset of promoters that possess its specific sequence elements. This specificity provides cells with the opportunity to activate whole batteries of genes in response to a given specific signal or stress.
d. Five Examples of transcription factors (eukaryotic) are: TFIIA, TFIIB, TFIIF, TFIIE, and TFIIH.
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