transport mechanisms. Determining precisely
which characteristics of a cage structure drive
this choice should prove interesting.
Whatever the answers to these questions,
. provide us with an intriguing new
structure that, like clathrin, helps cells solve
the problem of forming capsules of varying
size while precisely controlling their forma-
tion and contents. Further cryo–electron
microscopy maps could tell us the position of
other COPII coat components in relation to the
cage and, at higher resolutions, define the
location of individual Sec13p and Sec31p sub-
units, and the nature of the interactions that
define lattice assembly.
References and Notes
1. S. M. Stagg
, 234 (2006)
2. C. J. Smith, N. Grigorieff, B. M. Pearse,
3. A. Musacchio
, 761 (1999).
4. A. Fotin
, 573 (2004).
5. L. C. Bickford, E. Mossessova, J. Goldberg,
, 147 (2004).
6. G. Z. Lederkremer
Proc. Natl. Acad. Sci. U.S.A.
7. X. Bi, R. A. Corpina, J. Goldberg,