Fig. 1

The principle for a frame-shift fluorescence protein that is specifically activated by insertion/deletion (in/del) of nucleotides. See Additional file 1: Figure S1 for the details of the vector structure. As illustrated in the scheme, a target nuleotide sequence with the length of 3n +/− 1 (n > =1) is inserted between a start-codon (ATG) and the rest of the coding sequence of a fluorescence protein such as CFP. As such, this fluorescence protein is not expected to be translatable. However, if an in/del event takes place at the inserted target sequence, by a probability of about 1/3, the resulted sequence will become in frame for the translation of the fluoresence protein