How to Reverse Complement a DNA Sequence

Why the reverse complement matters

DNA has two strands that run in opposite directions. Sequences are written 5′ to 3′, so the other strand, read in its own 5′ to 3′ direction, is the reverse complement. You need it to design a reverse primer, to read a gene that sits on the minus strand, or to compare a sequencing read that came off the opposite strand.

Work it out by hand

1. Swap every base for its partner: A ↔ T and G ↔ C.
2. Read the result backwards.

For 5′-ATGCCTAG-3′ the complement is TACGGATC and the reverse complement is 5′-CTAGGCAT-3′. Reversing without complementing gives GATCCGTA, which is a different sequence and a common mistake.

Ambiguity codes and RNA

IUPAC codes have partners too: R (A or G) pairs with Y (C or T), K with M, and B, D, H and V pair with V, H, D and B. S, W and N stay as they are. In RNA, U takes the place of T.

Do it in the browser

1. Open Reverse Complement.
2. Paste one sequence, or many in FASTA format.
3. Pick reverse complement, reverse or complement. Titles, case and ambiguity codes are kept.

To change T to U instead, use DNA to RNA.