# Studies of DNA Licensing in Apicomplexa Parasites

> **NIH NIH R01** · UNIVERSITY OF SOUTH FLORIDA · 2020 · $526,152

## Abstract

Existing therapies, particularly against malaria, are under constant pressure from acquired parasite drug
resistance requiring a continuing search for new treatments. The peculiar proliferative cycles of Apicomplexa
parasites differ substantially from the hosts they inhabit and should offer fertile ground to supply an active
pipeline of new targets. To fulfill this promise, we need a better understanding of the unique structural and
molecular features of parasite cell division. Apicomplexan proliferation has adapted to different host cells using
chromosome replication cycles that can vary in the scale of nuclear reduplication from a few to hundreds of
nuclei produced per day, which is unparalleled cell cycle flexibility. How fidelity is preserved through variable
rounds of chromosome replication is a major mystery of Apicomplexa biology as many known regulators of
DNA replication in multicellular eukaryotes are missing in these parasites. Further, the basic checkpoint
mechanisms that regulate the cell cycle transitions are also poorly understood. It is not known what controls
G1 to S phase commitment, S phase progression, chromosome segregation or what controls allow the parasite
to forgo budding in one type of chromosome cycle but not in another during the processes of schizogony and
endopolygeny. In this application we will investigate several Toxoplasma mutants that carry lethal point
mutations in proteins essential for proper chromosome replication and segregation. When shifted to high
temperature these mutants all suffer very similar disruptions in chromosome replication. In Aim 1, we will
define the molecular function of a novel RING protein (ECR1, essential for chromosome replication 1) in
regulating chromosome replication and segregation. We will determine whether ECR1 is a divergent E3 ligase
and compare the molecular features of this mechanism in controlling DNA replication to the known
chromosome licensing factor Topo-II. We will also investigate an alternate role for ECR1 in regulating the
tachyzoite cell cycle. ECR1 forms a complex with a Toxoplasma ortholog of human cyclin-dependent kinase 2
(TgCDK2). The ECR1/TgCDK2 complex appears in the centrocone and then leaves this compartment to
become exclusively nuclear during S phase. We will characterize the molecular basis for this interaction and
determine whether this partnership is required for ECR1 function. We will also determine the basic features of
the TgCDK2 mechanism including whether it requires a cyclin for function and identify the protein substrates of
TgCDK2 in order to understand how this kinase mechanism regulates the tachyzoite S phase progression. In
Aim 2, we will investigate two chemical mutants harboring two other defective ECR factors (ECR2 and 3) that
also cause uncontrolled DNA synthesis when mutant parasites are grown at high temperature. ECR2 and
ECR3 are unknown proteins conserved only within Apicomplexa genetic lineages. The discovery of
apicomplexan-specific...

## Key facts

- **NIH application ID:** 9936121
- **Project number:** 5R01AI122760-05
- **Recipient organization:** UNIVERSITY OF SOUTH FLORIDA
- **Principal Investigator:** Michael W White
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $526,152
- **Award type:** 5
- **Project period:** 2016-06-14 → 2022-05-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9936121

## Citation

> US National Institutes of Health, RePORTER application 9936121, Studies of DNA Licensing in Apicomplexa Parasites (5R01AI122760-05). Retrieved via AI Analytics 2026-05-25 from https://api.ai-analytics.org/grant/nih/9936121. Licensed CC0.

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