Song of SecB

O lovely little nascent chain,
A protein soon you’ll be.
You’ll have to leave the ribosome
When it reads UAG.

Diffuse away! You cannot stay
But thanks to Brownian motion,
Before you know it you’re adrift
Upon the inner ocean.

I see you havea leader sequence
Tacked to your front end.
This means you’re going far from here,
My slowly folding friend.

If you will bind to all my sites,
I’ll change my conformation.
Then you’ll be well on your way
To membrane translocation.

Keep a lookout for SecA
For who I have affinity.
A dimer, tetramer and thou –
We three will form a trinity.

When we reach the membrane
I’ll dissociate.
But SecA will guide you safely
To your periplasmic fate.

One day when you’re far away
With ligands of your own,
Think of me, dear old SecB,
Your faithful chaperone.


– Virginia F. Smith,
published in the journal Trends in Biological Sciences, June 1998.