Figure: Database statistics representing the number of localization signals for distinct subcellular location along with the count of the research articles elucidating these signals. As seen, most studies have been done on inferring the protein localization signals for nucleus followed by mitochondria by a wide margin and all the other six organelles.

Figure: An overview of the frequency distribution of amino acids in the signal set for each of the eight subcellular organelles. As seen from the radar plots, there are clear differences in the frequency occurrence of amino acids for each distinct organelle. Nucleus is dominated by positively charged residues like lysines and arginines; whereas, mitochondrial signals have frequent occurrence of hydrophobic amino acids like: glycine, leucine and alanine as well as positively charged amino acids like arginine. Also, negatively charged amino acids like aspartic acid and glutamic acid are present only in the signals of organelles like Golgi and ER.