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: ["Gene"].

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

Isolation, characterization, and chromosomal mapping of a novel cDNA clone encoding human selenium binding protein. We have isolated the full-length human 56 kDa selenium binding protein (hSP56) cDNA clone, which is the human homolog of mouse 56 kDa selenium binding protein. The cDNA is 1,668 bp long and has an open reading frame encoding 472 amino acids. The calculated molecular weight is 52.25 kDa and the estimated isoelectric point is 6.13. Using Northern blot hybridization, we found that this 56 kDa selenium binding protein is expressed in mouse heart with an intermediate level between those found in liver/lung/kidney and intestine. We have also successfully expressed hSP56 in Escherichia coli using the expression vector-pAED4. The hSP56 gene is located at human chromosome 1q21-22).
{"Gene": ["selenium binding protein", "hSP56", "56 kDa selenium binding protein"]}