I found a lot of commercial plasmids are bidirectional, that they have genes in opposite direction. How does that work?
PS: See the attached, the arrows point to the opposite direction.
One gene is on one strand of the DNA and a gene in the opposite direction would be on the other strand. As far as the cell is concerned, there is no difference and there is no directionality. So long as each gene carries appropriate signals for transcription and translational they will work fine.
I attached a figure in the question. There are two directions for the genes.
Plasmids are made of double-stranded DNA. Protein-coding genes can encode the polypeptide chain on one or the other DNA strand. Likewise for non-coding genes.
@Michael @Ralf
So why don't people put the gene in one direction on one strand?
Because there is no reason to do so, it works equally fine either way. Remember that these plasmids are not entirely synthetic but were pieced together from segments found in nature, where genes are nearly always found on both strands of the DNA and therefore in both directions.
Professor Benedik, you have mentioned in your previous comment, "So long as each gene carries appropriate signals for transcription and translational they will work fine" are these signals always promoter? Thank you!
The promoter would be the minimal essential feature but for a gene to be translated one would also need the appropriate start signal and ribosome binding site. One also needs termination signals for both.
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