Transcribe DNA sequences into messenger RNA (mRNA). Convert template or coding strand to mRNA with automatic codon formatting.
Last updated: March 2026
Transcription is the first step in gene expression, where DNA is used as a template to synthesize messenger RNA (mRNA). In cells, RNA polymerase reads the template strand of DNA (3'→5' direction) and synthesizes a complementary mRNA strand (5'→3' direction).
DNA uses four bases: adenine (A), thymine (T), guanine (G), and cytosine (C). RNA also uses four bases, but replaces thymine with uracil (U). During transcription from the template strand, base pairing follows these rules: DNA A pairs with RNA U, DNA T pairs with RNA A, DNA G pairs with RNA C, and DNA C pairs with RNA G.
The coding strand (also called the non-template or sense strand) has the same sequence as the mRNA, except it contains T instead of U. This tool can convert either strand type: if you have the template strand, it performs complementary base pairing; if you have the coding strand, it simply replaces T with U.
The mRNA sequence is read in groups of three nucleotides called codons. Each codon specifies an amino acid during translation. This tool automatically formats the output into codons for easy reading.
Transcribe a template strand DNA sequence:
During translation, ribosomes read mRNA three nucleotides at a time. These groups of three nucleotides are called codons. The position where translation begins determines the reading frame. Shifting the reading frame by even a single nucleotide changes every downstream codon and usually produces a completely different protein.
| Reading Frame | Codons |
|---|---|
| Frame 1 | AUG GCU GAA |
| Frame 2 | UGG CUG AA... |
| Frame 3 | GGC UGA A... |
Even though these reading frames originate from the same nucleotide sequence, each produces a different series of codons. Functional protein-coding genes are translated in only one correct reading frame.
During transcription, RNA polymerase reads the DNA template strand in the 3'→5' direction while synthesizing a complementary mRNA strand in the 5'→3' direction.
Coding DNA 5' ATGCGATCG 3' │ Template DNA 3' TACGCTAGC 5' │ RNA Polymerase │ mRNA 5' AUGCGAUCG 3'
The coding DNA strand has the same sequence as the resulting mRNA except that DNA contains thymine (T) while RNA contains uracil (U).
This converter accepts only the four standard DNA nucleotides:
Ambiguous nucleotide symbols defined by the IUPAC nomenclature are not currently supported and are automatically removed before conversion. Examples include:
These symbols are commonly used in consensus sequences and degenerate PCR primers where multiple nucleotides may occur at a single position.
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RNA polymerase reads the template strand (3'→5') and synthesizes mRNA (5'→3') using complementary base pairing. The template strand is also called the antisense or non-coding strand. The other strand (coding/sense) has the same sequence as mRNA (except T→U).
RNA uses uracil (U) instead of thymine (T) for several reasons: U is simpler to synthesize (lacks a methyl group), U makes RNA less stable (beneficial for temporary messages), and this difference helps cells distinguish DNA from RNA for regulatory purposes.
AUG is the start codon (codes for methionine) that signals where translation begins. Stop codons (UAA, UAG, UGA) signal translation termination. Every protein-coding gene starts with AUG and ends with a stop codon.
This tool performs simple transcription of the input sequence. In eukaryotes, pre-mRNA undergoes splicing to remove introns and join exons. This tool doesn't perform splicing - it converts the exact input sequence provided.
The tool will still create codons, with the last group having fewer than 3 nucleotides. In real genes, coding sequences should be divisible by 3 (one complete reading frame). Incomplete codons usually indicate the sequence continues or there's an error.
Yes, reverse the process: replace U with T for the coding strand, or use complementary base pairing (U→A, A→T, G→C, C→G) to get the template strand. This reverse process doesn't naturally occur (except with retroviruses using reverse transcriptase).
This tool shows the primary transcript. In cells, mRNA undergoes modifications: 5' capping (m7G cap), 3' polyadenylation (poly-A tail), and various nucleotide modifications. These post-transcriptional modifications aren't represented in simple sequence conversions.
Human mRNAs range from ~300 nucleotides to over 100,000 nucleotides. Average protein-coding mRNAs are 1,500-2,000 nucleotides. The coding sequence (CDS) is typically 1,000-1,500 nt, but 5' UTR, 3' UTR, and poly-A tail add to total length.
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