You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Protein", "Chemical"].

Please return the output as a JSON object of the format: {"Chemical" : ["Dexamethasone", ...], "Protein" : ["BRCA-1", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

ATR regulates a G2-phase cell-cycle checkpoint in Arabidopsis thaliana.
Ataxia telangiectasia-mutated and Rad3-related (ATR) plays a central role in cell-cycle regulation, transmitting DNA damage signals to downstream effectors of cell-cycle progression. In animals, ATR is an essential gene. Here, we find that Arabidopsis (Arabidopsis thaliana) atr-/- mutants were viable, fertile, and phenotypically wild-type in the absence of exogenous DNA damaging agents but exhibit altered expression of AtRNR1 (ribonucleotide reductase large subunit) and alteration of some damage-induced cell-cycle checkpoints. atr mutants were hypersensitive to hydroxyurea (HU), aphidicolin, and UV-B light but only mildly sensitive to gamma-radiation. G2 arrest was observed in response to gamma-irradiation in both wild-type and atr plants, albeit with slightly different kinetics, suggesting that ATR plays a secondary role in response to double-strand breaks. G2 arrest also was observed in wild-type plants in response to aphidicolin but was defective in atr mutants, resulting in compaction of nuclei and subsequent cell death. By contrast, HU-treated wild-type and atr plants arrested in G1 and showed no obvious signs of cell death. We propose that, in plants, HU invokes a novel checkpoint responsive to low levels of deoxynucleotide triphosphates. These results demonstrate the important role of cell-cycle checkpoints in the ability of plant cells to sense and cope with problems associated with DNA replication.
{"Chemical": ["aphidicolin", "hydroxyurea", "HU", "deoxynucleotide triphosphates"], "Protein": ["AtRNR1", "Ataxia telangiectasia-mutated and Rad3-related", "ATR", "atr", "ribonucleotide reductase large subunit"]}