Tumor suppressor protein p53 is regulated in a number of ways, including during initiation of TP53 mRNA translation. The 5' end of TP53 mRNA contains regulatory structures that enable non-canonical initiation using mechanisms that remain poorly described. Here we analyze per-nucleotide reactivity changes in the 5' end secondary structure of TP53 mRNA under in-cell conditions using A549 human lung carcinoma cells. We first construct a cell-free secondary structure model using SHAPE reagent 5NIA (5-nitroisatoic anhydride) on gently extracted and deproteinated RNA. We observe previously described regulatory features of the TP53 mRNA 5' end including two motifs which we refer to as long stem-loop (LSL) and short stem-loop (SSL), respectively. We observe a domain-forming helix that groups LSL and SSL, forming a three-helix junction. Applying in-cell SHAPE-MaP, we assess reactivity profiles with unstressed cells and with chemically induced stress conditions expected to stimulate TP53 cap-independent translation. We analyze the effects of etoposide-induced DNA damage, CoCl