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Nuclear accumulation of Saccharomyces cerevisiae Mcm3 is dependent on its nuclear localization sequence
Author(s) -
Young Michael R.,
Suzuki Katsunori,
Yan Hong,
Gibson Susan,
Tye Bik K.
Publication year - 1997
Publication title -
genes to cells
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.912
H-Index - 115
eISSN - 1365-2443
pISSN - 1356-9597
DOI - 10.1046/j.1365-2443.1997.1510349.x
Subject(s) - biology , nuclear localization sequence , nls , nuclear transport , nuclear protein , cell nucleus , cell cycle , dna replication , microbiology and biotechnology , saccharomyces cerevisiae , origin recognition complex , nuclear export signal , eukaryotic dna replication , nucleus , biochemistry , cell , dna , gene , transcription factor
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.