Pre-replication complex organization in the atypical DNA replication cycle of Plasmodium falciparum: characterization of the mini-chromosome maintenance (MCM) complex formation.
The overall organization of cell division in Plasmodium is unique compared to that observed in model organisms because DNA replicates more than once per cell cycle at several points of its life cycle. The sequencing of the Plasmodium genome has also revealed the apparent absence of many key components (e.g. Cdt1, DDK and Cdc45) of the eukaryotic cell cycle machinery that are responsible for the formation of the pre-replication complex (pre-RC). We have characterized the Plasmodium falciparum minichromosome maintenance complex (MCM) that plays a key role in the transition of pre-RC to the RC. Similar to other eukaryotes, the Plasmodium genome encodes six MCM subunits. Here, we show that expression levels of at least three of the PfMCM subunits, the homologues of MCM2, MCM6 and MCM7, change during the intraerythrocytic development cycle, peaking in schizont and decreasing in the ring and trophozoite stages. PfMCM2, 6 and 7 subunits interact with each other to form a developmentally regulated complex: these interactions are detectable in rings and schizonts, but not in trophozoites. PfMCM2, 6 and 7 subunits are localized in both cytosolic and nucleosolic fractions during all intraerythrocytic stages of P. falciparum development, with increased nuclear localization in schizonts. Only PfMCM6 is associated with the chromatin fraction at all stages of growth. No phosphorylation of PfMCM2, 6 and 7 was detected, but two as yet unidentified threonine-phosphosphorylated proteins were present in the complex, whose pattern of phosphorylation varied during parasite development.
Patterson
Shelley
S
Department of Molecular Biology and Microbiology, University of Central Florida, Orlando, FL 32826, USA.
Robert
Claudia
C
Whittle
Christina
C
Chakrabarti
Ratna
R
Doerig
Christian
C
Chakrabarti
Debopam
D
D000595:Amino Acid Sequence; D000818:Animals; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002868:Chromosomal Proteins, Non-Histone; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004912:Erythrocytes / Q000469:parasitology; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D064151:Minichromosome Maintenance Complex Component 6; D064168:Minichromosome Maintenance Complex Component 7; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D051738:Origin Recognition Complex; D010963:Plasmodium falciparum / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment
D018797:Cell Cycle Proteins; D002868:Chromosomal Proteins, Non-Histone; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D009687:Nuclear Proteins; D051738:Origin Recognition Complex; D015800:Protozoan Proteins; D011994:Recombinant Proteins; D029701:Saccharomyces cerevisiae Proteins; C491207:MCM6 protein, S cerevisiae; C491088:MCM7 protein, S cerevisiae; D064151:Minichromosome Maintenance Complex Component 6; D064168:Minichromosome Maintenance Complex Component 7