George Gutman wrote:
>> Can anyone point me to any recent surveys of vertebrate
> and/or mammalian 5'
> and 3' NCRs, showing their size distributions?
I doubt we have a good understanding of this yet.
Most GenBank/EMBL/DDJP entries are either based on cDNAs
which are not proven to be complete at either the 5' or
3' end (thus we are usure of the size of the untranslated region)
or they are from DNA where the exact start of transcription
is unsure (thus we do not know the size of the untranslated
Add to that, the fact that many genes have been
found to have multiple origins of transcription and/or
multiple poly-adenylation sites.
Even if you are careful, and take only those
database entries for which transcription and translation
start and stop points are known, you may have a highly
biased data set. It may be much easier to define these
sites on genes with shorter untranslated regions.
In general, eukaryotic messenger RNAs are
translated into protein beginning at the first
ATG codon encountered. This will tend to limit the
size of the 5' untranslated region. Poly-adenylation
is less clearly defined, and therefor the 3'
untranslated region is apt to be able to be much
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