Polyadenylation (or Poly(A)) signal, site and tail
The polyadenylation or Poly(A) is the process required for the synthesis of messenger
RNA (mRNA) in which an endonucleolityc RNA cleavage is coupled with synthesis
of polyadenosine monophosphate (adenine base) on the newly formed 3' end. The sequence elements
for polyadenylation include the polyadenylation signal (POLYA_SIGNAL) and the
polyadenylation site (POLYA_SITE). In mRNA or cDNA the added stretch of polyadenosine monophosphate
is the polyadenylation tail (POLYA_TAIL).
- Poly(A) signal
- IMGT label: POLYA_SIGNAL
- Conserved motif: AATAAA
- The polyadenylation signals are located downstream of the 3' exons .
- Example: A POLYA_SIGNAL located 103 bp downstream of the human IGHG3 CH3-CHS
exon is used in the transcription of
secreted gamma3 chains.
A POLYA_SIGNAL located downstream of the human IGHG3 M2 exon is used
in the transcription of membrane gamma3 chains .
- Poly(A) site
- IMGT label: POLYA_SITE
- The polyadenylation site is the site of cleavage at which POLYA_TAIL is added in
mRNA. It is localized downstream of the POLYA_SIGNAL. The POLYA_SITE can
be determined by comparing cDNA and gDNA.
- The sequence at/or immediately 5' to the site of RNA cleavage is frequently (but
not always) CA. A 'G-U-rich' element or Downstream element usually lies just downstream of
the POLYA_SITE in gDNA, which is important for efficient processing. In those cases, the POLYA_SITE
maybe located in gDNA.
- Poly(A) tail
- IMGT label: POLYA_TAIL
- Stretch of adenosine monophosphate (with only adenine bases) at the 3' end of mRNA or cDNA.