Control of embryonic gene translation

[keenangp]

Hey, first time posting here, but I've been lurking around the boards since before I got into Uni Bio.

So here's my question (semester break=no prof )

I've been told that sometimes during embryonic development [eukaryotic], or plants in a state of dormancy (assuming spores as well?), that mRNA processing will yield an incomplete poly'A tail, which disallows the binding of the ribosomal subunit etc. When development is triggered, an enzyme will complete the Poly'A tail, allowing for the binding of the small ribosomal sub-ubit, and thus translation.

This threw me for a loop, because I believe the ribosomal sub-unit binds to the 5' cap, moving in a 5'->>3' direction?

So here I remembered a clip from the boys and girls at harvard which showed an mRNA during translation as circular, but it was the first time we had seen it like that. I'm hypothesizing that the translation initiation complex depends on the poly'A tail because the ends are in contact. I havn't a clue though.. Please shed some light on the situation.

Thanks!

PS: I know during RNA degradation the ends are brought in contact, so this kind of gave the idea some validity.

[MrMistery]

I'm glad you watched Rob Lue's animation. Isn't it cool?
Now, the ends are brought together so that a ribosome, after it has finished translation of the mRNA and has broken apart into the two ribosomal subunits, the subunits will be in an ideal position to re-associate and start the cycle again. this increases the amount of protein made from an mRNA molecule. However, this does not mean that the poly-A tail is required for translation initiation. It's not.
What I think is occuring is that the mRNA with the incomplete poly-A tail is not getting exported from the nucleus. I say this from three reasons:
1. I think I remember reading that the poly-A-binding protein is one of the receptors for nuclear export
2. If this were not the case, the mRNAs with short tails would soon be degraded(the tail generally keeps the mRNA from being degraded too fast)
3. Poly-A polymerase and the proteins that recruit it to the mRNA are only located in the nucleus. If the mRNA was in the cytoplasm, then upon receiving the signal the mRNA would have to be transported back into the nucleus, and that simply doesn't happen.

Cheers.