Dear Rachel,

According to the brochure that I attached to this message (pET28.pdf):

"The maps for pET-28b(+) and pET-28c(+) are the same as pET-28a(+) (shown) with the following exceptions: pET-28b(+) is a 5368bp plasmid; subtract 1bp from each site beyond BamH I at 198. pET-28c(+) is a 5367bp plasmid; subtract 2bp from each site beyond BamH I at 198."

Basically, I think you can choose either of the two plasmids. I hope this answers your question.

Best regards,

Tomás

Tomás Monteiro Fernandes ah okay. Thank you so much!

pET series vecor is engineered vector. Then why Scientists made such type of difference? What is the significance behind this changes?

the reading frame changes

Okay.Thank You.

While using pET28 series, there shouldn't be a problem when one of the cloning sites chosen are away from MCS (eg) Nde1, Nhe1, Bmt1, Nco1. In such cases, pET28a or pET28b or pET28c can be used. There would be no frame shift in such cases.

Whereas, when the chosen cloning site lies within the MCS of the plasmid, each variant of the plasmid has a different reading frame. The variation is introduced just ahead of the BamH1 site.

In between, T7 tag and BamH1 site,

'CGC' - Three nucleotides in pET28a - (5369bp);

'CG' - Two nucleotides in pET28b - (5368bp);

'C' - One Nucleotide in pET28c (5367bp) can be noticed contributing to the shift in reading frame.

And hence, it is important to strategize cloning according to the availability of the respective plasmid.

Hope this helps !