Eye Candy

I gave lab meeting yesterday and I'm exhausted. Here something I presented.

(First the images then the explanation)

Image 1:

Image 2:

Signal sequences are short stretches of protein that are recognized by the signal recognition particle and direct the protein to be inserted into the endoplsmic reticulum (ER). Similarly there are protein stretches that target newly synthesized proteins to mitochondria. Signal sequences are hydrophobic, while mitochondrial targeting sequences are amphipathic helices.

What is an amphipathic helix? Poly-peptide chains tend to either line up next to each other to form beta-sheets of twist to form alpha-helices. In an amphipathic helix, the residues one one side are hydrophobic, while residues on the other side are hydrophilic or even charged.

The experiment: I microinjected mRNA that encodes a protein that normally is destined to be inserted into the ER (see image 2), but whose signal sequence has been altered with three charged residues. In the top image RNA from the altered gene is microinjected into a tissue culture cell (the inset shows injection marker that labels the microinjected cell - note that the RNA was microinjected into the nuclei, and thus the injection marker is confined to the nuclei of the injected cell). The top panel (in image 1), is the a micrograph of the translated protein with the altered signal sequence. The protein now gets inserted into "mitos" . The bottom panel of image 1 is a phase micrograph of that very same field of cells (form more on phase contrast microscopy, click here). Unlike the endoplasmic reticulum, you can see the mitos by phase (they are the phase dense objects).

So you see, with a simple 3 point mutation you can direct a protein that is destined for the ER into mitos.