The effe
cts of purified re
combinant mi
crotubule-asso
ciated protein2
c (rMAP2
c) on the dynami
cinstability of mi
crotubules were examined by dire
ct observation ofindividual mi
crotubules
in vitro byvideo-enhan
ced differential interferen
ce
contrast light mi
cros
copy.Mi
crotubules were grown in the absen
ceor presen
ce of varying
con
centrations of rMAP2
c and were analyzed todetermine growth rates, shorteningrates,
and the frequen
cies of
conversion between growing
and shorteningphases. We found rMAP2
c tostabilize mi
crotubules dramati
cally. The most notable effe
ct is aredu
ction in both the frequen
cy of
catastrophes (transitions from growth to shortening)
and the meanlength of shortening events: nomi
crotubule
catastrophes were observed at
con
centrations of rMAP2
c aslow as 1.06
![](/images/entities/mgr.gif)
M in a solution of10
![](/images/entities/mgr.gif)
M tubulin. Even at lower rMAP2
c con
centrations, there is amarked stabilizing effe
ct. As the
con
centration of rMAP2
c in
creases, average growth rates in
creaseslightly, shortening rates de
crease,
andthe frequen
cy of res
cues (transitions from shortening to growth)in
creases signifi
cantly. Together, these
changes in parameters produ
ce a population of extremely stablemi
crotubules in the presen
ce of rMAP2
c.This stabilization is
consistent with a stru
ctural role for MAP2
cduring early postnatal neural development.