issues when designing PCR primers using PRIMER3 - (Oct/16/2012 )

When I was designing primers using PRIMER3
The screen outputs like follows
Forward primer ACTGACTG
Reverse primer CTGACTGA

I was wondering do I need to reverse and complement my reverse primer when ordering my primers?

For example, I should order TCAGTCAG for my real reverse primer
Thank you.

Primer3 should give you the sequence as you would order it (i.e. already reverse complemented). If you look at where the program shows the primers to be according to the sequence you submitted, the reverse primer should show the reverse complement of the sequence.

Thank you. I use NCBI primerBLAST. It uses primer3.
I assume the output of the reverse primer need not to be changed, right?
the output look like this:
sequence 5'-3'
Forward primer ACTGACTG
Reverse primer CTGACTGA
So I should directly order as above? right?

Yep.

Yes, bob1 is right, Both Primer3 and NCBI-Primer BLAST gives hte primers in 5'-3' direction. As far as I know Primer Express also gives it in 5'-3' format.

K.

Also easy way to check this is to try and find the primers in input sequence. You should find there forward primer, but not the sequence of reverse. If you use some online reverse-complement tools on your reverse primer, you should now be able to find it in the sequence.
(but note it's just common agreement to call the first primer on the sequence forward and second reverse, and all common primer designing tools do it this way, but in some special circumstances reversed orientation of the first primer on sequence could be choosen and also corresponding with that, the second primer orientation would be identical to input sequence, but in that case it would be appropriate to call the first primer reverse and the second forward, but you can always blast the primers and check whether they are on the same sequence in opposite directions )

And last note, primer 3 displays the position of both primers ranked 1 on a input sequence, you it's most easier to check it there.

Thanks for all.

weihua on Tue Oct 16 22:10:37 2012 said: