The authors find that CsrA negatively regulates NleA express

The authors find that CsrA negatively regulates NleA expression, but positively other genes present in the LEE locus.

a. How could the same protein regulate one gene positively and another negatively?

b. Describe some molecular mechanisms that might allow this (what kinds of proteins could it interact with, etc.).

c. Would you consider both upregulated and downregulated genes to be in the same regulon? Why?

Reading reference: http://science.sciencemag.org/content/sci/suppl/2017/02/15/355.6326.735.DC1/Katsowich.SM.pdf

& Host cell attachment elicits posttranscriptional regulation in infecting enteropathogenic bacteria

Solution

ANSWER:

a. An operon is a cluster of coordinately regulated genes.The type of control is defined by the response of the operon when no regulatory protein is present.

negative control, the genes in the operon are expressed unless they are switched off by a repressor protein. Thus the operon will be turned on constitutively when the repressor in inactivated.

positive control, the genes are expressed only when an active regulator protein, e.g. an activator, is present. Thus the operon will be turned off when the positive regulatory protein is absent or inactivated.

b.transcriptional and posttranscriptional mechanisms

c.a gene is upregulated or downregulated does not mean that the process, function or component that the gene is annotated to is also respectively directionally regulated.