All genes in an operon are under the control of the same promoter, so will there be difference in the expression of the genes? Are there any reports on this?
Hi Victoria
There can be great differences. If the genes are expressed from a single promoter, then the RNA levels of each gene obviously will be the same. However, RNA secondary structure, strength of ribosomal binding site and codon usage can greatly influence the amount of protein translated from each gene. In addition, there have been several reports on how small non-coding RNAs can regulate protein translation in a discoordinated fashion (see for example: http://www.ncbi.nlm.nih.gov/pubmed/12101127). Similarly, recent transcriptome analysis by NGS sequencing have revealed a whole bunch of overlapping transcripts which seem to have different effects on the expression of operons
(http://www.ncbi.nlm.nih.gov/pubmed/23268228).Finally, many operons contain more than one transcriptional start sites. Some of these are alternative, stress responsive promoters which can be placed within the operon and thereby generate mRNAs that do not encompass the entire operon.
hope this helped
Jesper
Viral genes under the same promoter can be processed differently to yield different products. While transcription per se is the same, expression (as measured by abundance) may differ based on stability and processing.
Hi Victoria
There can be great differences. If the genes are expressed from a single promoter, then the RNA levels of each gene obviously will be the same. However, RNA secondary structure, strength of ribosomal binding site and codon usage can greatly influence the amount of protein translated from each gene. In addition, there have been several reports on how small non-coding RNAs can regulate protein translation in a discoordinated fashion (see for example: http://www.ncbi.nlm.nih.gov/pubmed/12101127). Similarly, recent transcriptome analysis by NGS sequencing have revealed a whole bunch of overlapping transcripts which seem to have different effects on the expression of operons
(http://www.ncbi.nlm.nih.gov/pubmed/23268228).Finally, many operons contain more than one transcriptional start sites. Some of these are alternative, stress responsive promoters which can be placed within the operon and thereby generate mRNAs that do not encompass the entire operon.
hope this helped
Jesper
thank you all for the answers.. i might not have been clear about my question.
I particularly want to know about the mRNA levels of the genes in an operon. I have expressed 2 genes from an operon in plasmid under the same promoter, but when I carried out mRNA studies of the individual genes, I observed a difference in their mRNA levels. Ideally they should be same. Is there any explanation for the difference?
Could you add the type of cells under investigation? (to predict a possible mechanism) The stability of individual mRNAs could affect their steady state concentration. One of your mRNAs could turn-over faster than the other.
I am assuming you are comparing relative concentration of each mRNA to a known concentration of the same mRNA. If you are conducting qRT-PCR the efficiency of RT for each RNA will be different. So you need to have a standard curve (or reference point) set for each mRNA using its own cDNA control. Comparison without this standard would lead to comparing the (relative expression level+ difference in RT), which could be misleading.
@ Prakash Chandra The 2nd mRNA level higher than first.
@ Sathiya Manivannan - Its a bacterial cell. Yes I am comparing the relative concentration of each mRNA to a known concentration of the same mRNA
@Victoria: It is possible that the second mRNA is more stable than the first mRNA. There are secondary structures within mRNA that make one mRNA more stable than the other. Are there possible riboswitches in your mRNAs?
These findings can be explained by a common mechanism; increasing the distance from the start of a gene to the end of the operon (termed the “transcription distance”) provides more time for translation to occur during transcription, resulting in increased expression.
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