Tp. Spann et al., DISRUPTION OF NUCLEAR LAMIN ORGANIZATION ALTERS THE DISTRIBUTION OF REPLICATION FACTORS AND INHIBITS DNA-SYNTHESIS, The Journal of cell biology, 136(6), 1997, pp. 1201-1212
The nuclear lamina is a fibrous structure that lies at the interface b
etween the nuclear envelope and the nucleoplasm. The major proteins co
mprising the lamina, the nuclear lamins, are also found in foci in the
nucleoplasm, distinct from the peripheral lamina. The nuclear lamins
have been associated with a number of processes in the nucleus, includ
ing DNA replication. To further characterize the specific role of lami
ns in DNA replication, we have used a truncated human lamin as a domin
ant negative mutant to perturb lamin organization. This protein disrup
ts the lamin organization of nuclei when microinjected into mammalian
cells and also disrupts the lamin organization of in vitro assembled n
uclei when added to Xenopus laevis interphase egg extracts. In both ca
ses, the lamina appears to be completely absent, and instead the endog
enous lamins and the mutant lamin protein are found in nucleoplasmic a
ggregates. Coincident with the disruption of lamin organization, there
is a dramatic reduction in DNA replication, As a consequence of this
disruption, the distributions of PCNA and the large subunit of the RFC
complex, proteins required for the elongation phase of DNA replicatio
n, are altered such that they are found within the intranucleoplasmic
lamin aggregates. In contrast, the distribution of XMCM3, XORC2, and D
NA polymerase alpha, proteins required for the initiation stage of DNA
replication, remains unaltered. The data presented demonstrate that t
he nuclear lamins may be required for the elongation phase of DNA repl
ication.