RNA Caps and Tails
What are the possible biological roles of the cap and
poly-A tail in mRNA?
Experiments have clearly shown that the poly-A tail on a mRNA is to prevent
it from being dismantled in the cytosol of the cell by enzymes when it leaves the
nucleus. RNAs without this tail are quickly dismantled and with the string
of A's[as many as 200!], may last for 24 hours or more.
The modified guanine nucleotide at the head of the messenger RNA [mRNA]
identifies the molecules as a mRNA. It is a chemical signal as to what the
molecule's function is to be. The other two types of RNA [ribosomal
RNA(rRNA) and transfer RNA (tRNA)] appear to have chemical signaling to
indicate their function as well. However, I must note that this chemical
signaling has not be demonstrated conclusively as yet. Feb. 2000
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Update: June 2012