Hi

Signal sequence for promoters are situated at -10 and at -35 bp (Upstream) from the first nucleotide of start codon. If I remember it right, sigma factor interacts with -10 upstream sequence and C-terminals of alpha subunits interact with -35 region of the promoter. So the optimum distance between a promoter and a start codon is not more than 18-20bp. However, I assume here that you are talking about  a bacterial expression system.

Hope this helps...

Good luck :)

Hi Shridhar,

Thanks very much for your answer, I will actually be using the plasmid to express the transgene in mammalian cells, I probably should have mentioned that in the question.

All the best,

Shaun

The -10 and -35 boxes of the promoter are designated defining as +1 the transcription initiation nucleotide not the start codon.

I agree with Panagiotis, the start codon is in the context of translation whereas the -10 and -35 positions are for transciption.