(A) Mutation patterns, including mutations of (G)7 and (C)6 runs in the TK domain in sequenced Gc-r clones; (B) mutation patterns without mutations of (G)7 and (C)6 runs in sequenced Gc-r clones. Statistical significance of the differences was verified by Fisher standard test. Treatment of the clone carrying CGG153-HyTK cassette with of Pold3 siRNA wipes out complex mutations.