TY - JOUR
T1 - Nuclear accumulation of Saccharomyces cerevisiae Mcm3 is dependent on its nuclear localization sequence
AU - Young, Michael R.
AU - Suzuki, Katsunori
AU - Yan, Hong
AU - Gibson, Susan
AU - Tye, Bik K.
PY - 1997
Y1 - 1997
N2 - Background: The proteins of the Mcm2-7 family are required for the initiation of DNA replication. In Saccharomyces cerevisiae the nuclear envelope does not break down during the mitotic phase of the cell cycle. Large nuclear proteins, such as the Mcm proteins, which accumulate in the nucleus during specific portions of the cell cycle, must have regulated mechanisms to direct their entry into the nucleus. Results: We have identified a nuclear localization sequence (NLS) in Mcm3, and demonstrated that it is necessary for the translocation of Mcm3 into the nucleus and sufficient for directing Escherichia coli β-galactosidase to the nucleus. Immediately adjacent to the nuclear localization sequence are four potential sites for phosphorylation by Cdc28. Mutagenesis of all four sites has no immediate phenotypic effect on cell growth or viability, nor does it affect nuclear accumulation of Mcm3, although two-dimensional protein gel analysis has shown that at least some of these sites are normally phosphorylated in vivo. Substitution of the Mcm3 NLS by the SV40 large T-antigen NLS also directs the nuclear accumulation of the Mcm3-T-antigen protein, although cell growth is compromised. Replication activity in cells bearing either the Mcm3-Cdc28 phosphorylation site mutations or the Mcm3 T-antigen NLS substitution, as measured by plasmid stability assays, is comparable to activity in wild-type cells. Conclusions: The Mcm3 protein is imported into the nucleus by a specific NLS. The cell cycle specific nuclear accumulation of Mcm3 appears to be a result of nuclear retention or nuclear targeting, rather than nuclear import regulated through the NLS.
AB - Background: The proteins of the Mcm2-7 family are required for the initiation of DNA replication. In Saccharomyces cerevisiae the nuclear envelope does not break down during the mitotic phase of the cell cycle. Large nuclear proteins, such as the Mcm proteins, which accumulate in the nucleus during specific portions of the cell cycle, must have regulated mechanisms to direct their entry into the nucleus. Results: We have identified a nuclear localization sequence (NLS) in Mcm3, and demonstrated that it is necessary for the translocation of Mcm3 into the nucleus and sufficient for directing Escherichia coli β-galactosidase to the nucleus. Immediately adjacent to the nuclear localization sequence are four potential sites for phosphorylation by Cdc28. Mutagenesis of all four sites has no immediate phenotypic effect on cell growth or viability, nor does it affect nuclear accumulation of Mcm3, although two-dimensional protein gel analysis has shown that at least some of these sites are normally phosphorylated in vivo. Substitution of the Mcm3 NLS by the SV40 large T-antigen NLS also directs the nuclear accumulation of the Mcm3-T-antigen protein, although cell growth is compromised. Replication activity in cells bearing either the Mcm3-Cdc28 phosphorylation site mutations or the Mcm3 T-antigen NLS substitution, as measured by plasmid stability assays, is comparable to activity in wild-type cells. Conclusions: The Mcm3 protein is imported into the nucleus by a specific NLS. The cell cycle specific nuclear accumulation of Mcm3 appears to be a result of nuclear retention or nuclear targeting, rather than nuclear import regulated through the NLS.
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U2 - 10.1046/j.1365-2443.1997.1510349.x
DO - 10.1046/j.1365-2443.1997.1510349.x
M3 - Article
C2 - 9427284
AN - SCOPUS:0031240843
SN - 1356-9597
VL - 2
SP - 631
EP - 643
JO - Genes to Cells
JF - Genes to Cells
IS - 10
ER -