The molecular interactions responsible for nuclear envelope assembly after
mitosis are not well understood. In this study, we demonstrate that a pepti
de consisting of the COOH-terminal domain of Xenopus lamin 83 (LB3T) preven
ts nuclear envelope assembly in Xenopus interphase extracts. Specifically,
LB3T inhibits chromatin decondensation and blocks the formation of both the
nuclear lamina-pore complex and nuclear membranes. Under these conditions,
some vesicles bind to the peripheral regions of the chromatin. These "nonf
usogenic" vesicles lack lamin B3 (LB3) and do not bind LB3T; however, "fuso
genic" vesicles containing LB3 can bind LB3T, which blocks their associatio
n with chromatin and, subsequently, nuclear membrane assembly. LB3T also bi
nds to chromatin in the absence of interphase extract, but only in the pres
ence of purified LB3. Additionally, we show that LB3T inhibits normal lamin
polymerization in vitro. These findings suggest that lamin polymerization
is required for both chromatin decondensation and the binding of nuclear me
mbrane precursors during the early stages of normal nuclear envelope assemb
ly.