Regulatory roles of the nuclear envelope.
Roles of the nuclear envelope are considered in the regulation of nuclear protein import, ribonucleoprotein export, and coupling of DNA replication to the cell cycle. First, evidence is discussed that indicates that neutral and acidic amino acids can be important in nuclear localization signals as well as the widely acknowledged basic amino acids. Second, the recognition of nuclear localization signals by their receptor "importin" is discussed, focusing on the different roles of the two subunits of importin. Third, a role for the alpha subunit of importin in RNP export is considered together with the question of how the direction of traffic through nuclear pores is determined. The final part of this article considers evidence that the nuclear membrane prevents reinitiation of DNA replication in Xenopus eggs, by excluding a "licensing factor" that is essential for DNA replication. Replication licensing in Xenopus appears to involve several proteins including the MCM (minichromosome maintenance) complex and ORC, the origin recognition complex, which must bind before the MCM complex can bind to chromatin.
Laskey
R A
RA
Wellcome/CRC Institute, Tennis Court Road, Cambridge, CB2 1QR, United Kingdom.
Görlich
D
D
Madine
M A
MA
Makkerh
J P
JP
Romanowski
P
P
D000595:Amino Acid Sequence; D000818:Animals; D001693:Biological Transport, Active; D002453:Cell Cycle; D002843:Chromatin / Q000378:metabolism; D004261:DNA Replication; D005260:Female; D028884:Karyopherins; D008954:Models, Biological; D009685:Nuclear Envelope / Q000378:metabolism*; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D010063:Ovum / Q000378:metabolism; D018741:Replication Origin; D014981:Xenopus
D002843:Chromatin; D028884:Karyopherins; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins