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: ["RNA", "CellLine", "Protein", "DNA", "CellType"].

Please return the output as a JSON object of the format: {"DNA" : ["TAL1", ...], "RNA": ["mRNAs", ...], "CellLine": ["T cells", ...], "CellType": ["monocytes", ...], "Protein": ["IL-2", ...]}. 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:

Identification of transcriptional suppressor proteins that bind to the negative regulatory element of the human immunodeficiency virus type 1. Two different proteins which independently bound to neighboring sequences within the negative regulatory element (NRE) of human immunodeficiency virus type 1 (HIV-1) were detected in the nuclear extract of a virus-infected human T cell line. One of the factors bound to a novel dyad symmetrical sequence. This sequence is well conserved in various HIV-1 isolates and partial homology was found with the promoter region of the human retinoblastoma gene. Similar DNA binding activity was detected in a variety of virus-uninfected human T cell lines and HeLa cells by means of a gel mobility shift assay. The other factor bound to a putative AP-1 recognition sequence predicted for the HIV-1 NRE. However, this factor did not bind to a typical AP-1 site. The insertion of multiple copies of the binding site for the former or latter factor into a heterologous promoter reduced the promoter activity to one-tenth or one-third, respectively. Thus, each factor may function as a novel negative regulator of transcription.
{"CellLine": ["virus - infected human T cell line", "virus - uninfected human T cell lines", "HeLa cells"], "CellType": [], "DNA": ["heterologous promoter", "binding site", "AP - 1 site", "putative AP - 1 recognition sequence", "human retinoblastoma gene", "promoter region", "novel dyad symmetrical sequence", "negative regulatory element", "NRE"], "Protein": ["transcriptional suppressor proteins", "novel negative regulator"], "RNA": []}