Three major types of insect herbivores

Phloem feeders, such as aphids and whiteflies, cause little damage to the epidermis and mesophyll cells. Phloem feeders insert their narrow stylet, which is an elongated mouthpart, into the phloem sieve tubes of leaves and stems. 

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p53

tumor-suppressor gene 

arrest of cells with damaged DNA

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p53

extremely unstable protein and generally does not accumulate to high enough levels to stimulate transcription under normal conditions

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MDM2

catalyzes the ubiquitinylation of p53 & targeting it for proteasomal degradation

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Rapid degradation of p53 is inhibited by ATM and ATR, after DNA damage

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Phosphorylation of p53 on a serine residue in the N-terminus by ATM or DNA-PK displaces bound MDM2 from p53, thereby stabilizing it

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MDM2 levels in the cytoplasm are controlled by

ATR and p14ARF (p19ARF in the mouse), sequesters it in the nucleolus, where it cannot access p53.