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: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. 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:

Evidence for self-association of the alternative sigma factor σ54. Sigma factor σ(54) has a distinct modus operandi for mediating the activation of bacterial RNA polymerase (RNAP) at promoter recognition motifs 12 and 24 bp upstream from transcription start sites. σ(54) was thought to act as monomer in all transcription steps. However, we provide evidence that σ(54) of Pseudomonas putida interacts stably with itself. The interface between monomers involves contacts in σ(54) regions I and III, sequences that play key roles in the transcription activation of σ(54)-RNAP holoenzyme. These roles include interactions with activator proteins and the -12 and -24 motifs. In particular, we detected inter-monomer contacts between region I, and between region I and the C-terminal portion of region III. Our results suggest a new auto-antagonistic regulatory state of σ(54).
{"Chemical": ["C"]}