Summary
- The process of transcription synthesizes an RNA molecule that is complementary to the template strand of the gene. But it is identical to the nontemplate strand in both 5’ to 3’ polarity and sequence, with the substitution of U in the RNA for T in the DNA.
- Some RNA molecules encode protein sequences and will later be used in translation (mRNAs). Other RNA molecules function directly in different cellular processes.
- Transcription of a gene requires DNA elements that signal where the transcription machinery binds to the DNA, where transcription begins, and where transcription ends. These sequences are summarized in Table 2. Many of these DNA elements are bound by protein factors that facilitate transcription.
| No Data | Transcription machinery is first recruited to | The RNA molecule begins with | The RNA molecule ends with |
| Prokaryotes | -10 and -35 boxes in the promoter
(bound by σ factor) |
+1 nucleotide | The last base of the terminator |
|---|---|---|---|
| Eukaryotes | TATA box in the promoter
(bound by TATA-binding protein, part of TFIID) |
+1 nucleotide | The poly-A cleavage site followed by a long stretch of untemplated A’s |
- In eukaryotes, the primary transcript produced by RNA polymerase II is processed to become a mature mRNA. Processing includes the addition of a 5’ cap, the addition of a poly-A tail, and splicing to remove introns.
- Alternative splicing allows multiple mature mRNAs (and, later, multiple distinct proteins) to be produced from a single gene.
