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. 2012 Jan 19;7(1):e30437. doi: 10.1371/journal.pone.0030437

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Arrow shows the direction and start of transcription. L, loxP site. F, FRT site. P[en3R] is from [21] (called P[en1] in that study). P[en3] and P[en3Δboth] are from [18].