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It's maybe a stupid question, but I really want to know the answer.

The definition of Promoter (From Wikipedia):

In genetics, a promoter is a region of DNA that initiates transcription of a particular gene. Promoters are located near the transcription start sites of genes

And the definition of the transcription start site (From Wikiversity):

The transcription start site "is the location where transcription starts at the 5'-end of a gene sequence.

I also Found this image (The source):

enter image description here

I'm asking this question because as far as I know, the RNA Polymerase binds to the TSS, and a friend of mine told me that's it binds to the Promoter.

PS : I'm interested in bacteria.

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    $\begingroup$ You might be interested in this. $\endgroup$ – another 'Homo sapien' Apr 20 '17 at 8:31
  • $\begingroup$ From what I remember the promoter is not necessarily transcribed and not necessarily close to the Gene being transcribed, but somehow brings RNA pol to the right place, i.e. the TSS... I'm not sure it's a hard and fast rule though. $\endgroup$ – Oliver Houston Apr 20 '17 at 11:28
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You will find the answer to this question in any standard text book of Biochemistry, Molecular Biology or Molecular Genetics. There are several on-line at NCBI bookshelf, and these are generally far better than Wikipedia. I quote from section 28.1 of Berg et. al., dealing with transcription:

Transcription starts at promoters on the DNA template. Promoters are sequences of DNA that direct the RNA polymerase to the proper initiation site for transcription.

This is then followed by a description of prokaryotic promotor sequences and the consensus TATA box.

A striking pattern is evident when the sequences of many prokaryotic promoters are compared. Two common motifs are present on the 5′ (upstream) side of the start site. They are known as the -10 sequence and the -35 sequence because they are centered at about 10 and 35 nucleotides upstream of the start site.

Consensus promotors and TATA boxes

The methodology by which this was established is described, from which it becomes evident that another way of regarding the promotor is the site on the DNA at which the RNA polymerase binds.

From the embolded part of the quotation above (my emphasis), the promotor is clearly before (5′) of the start site. This is summarized in another small graphic:

Summary of promotor and transcription start site

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  • $\begingroup$ Sorry if this is an east question to answer but, what designates a specific part of the DNA to be the “transcription start site”? $\endgroup$ – Hawkeye Apr 11 '18 at 2:26
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Just in addition to David's answer, there are examples of internal promoters (those which have elements 3' of the transcription start site). As an example, internal promoter elements of tRNA genes direct binding of and transcription by eukaryotic RNAP III:

White RJ. 2011. Transcription by RNA polymerase III: more complex than we thought. Nature Rev Genet 12:459-463.

enter image description here

Many class I retrotransposons also contain internal promoters which allows them to be transposed along with the other elements:

  • LINE - internal RNAP II promoter
  • SINE - internal RNAP III promoter
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