Transcription and RNA Processing

ID #2396

So we learned that the -10 and -35 sites are needed for transcription to occur. Are these sites the same for every gene? Or will specific genes have different sequences? Is the -10 and -35 site universal but the sequences vary for different genes? Is there anything that controls transcription or will it continuously occur as long as the holoenzyme finds the site it's looking for?


The -10 and -35 sites are different for different genes. No gene has a consensus -10 or -35 site, but the closer the promoter sequence is to the consensus, the more transcription will occur. So yes, different genes will have different sequences.
The -10 and -35 sites you learned in lecture are the consensus sites. If you look at slide 7 of lecture 16, you can see examples of actual promoter sequences, with the -10 and -35 highlighted. The consensus is then listed underneath. 
For instance, the first base of the -10 sequence is not always "T" - in one of the examples, it is a C instead. But it is T more often than anything else, so the consensus for that site is T. 
By comparing the different sequences, we can work out the consensus based on what is most commonly found at that position. 
As I said above, real promoters vary between different genes, so it is necessary to compare many examples to determine which bases are conserved. 
Transcription is controlled by other factors - we will spend some time later in the course examining how an E. coli cell controls transcription of the genes needed to metabolize the disaccharide lactose. The exact form of this control depends on the gene you are interested in.
I realize this answer is a bit vague, but the regulation of transcription can be extremely complicated and the exact mechanism is different for different genes. That said, some genes are constitutively expressed - their promoters are so strong (and the proteins they encode for are so important to the cell) that they will be transcribed as long as there is available holoenzyme.

Print this record Print this record
Send to a friend Send to a friend
Show this as PDF file Show this as PDF file
Export as XML-File Export as XML-File