Cells were resuspended with 80 µl Antibody Buffer (mix 4 µL 0.5 M EDTA with 1 mL 0.01% Digitonin-Wash Buffer (Dig-Wash Buffer) supplemented with cocktail, 10 mM sodium butyrate and 0.05% Triton X-100) containing 0.4 µg primary antibody. The mixture was incubated at 4°C for 4 h in a rotator with 30 rpm. Cells were then washed twice with 180 µL Dig-Wash Buffer. The secondary antibody was incubated in the same buffer and condition except for the duration of 10 min. After washing with Dig-Wash Buffer twice, cells were suspended with 80 µl Dig-Wash Buffer (with 0.05% Triton-X, cocktail, and 10 mM sodium butyrate) containing 0.83 µM PAT-MEA/B at 4°C for 1 h. The free PAT-MEA/B were then dislodged with 180 µL Dig-Wash Buffer containing 0.05% Triton X-100 three times at 5 min each time. The reaction was activated by suspending the cells with 10 µL Reaction Buffer (10 mM TAPS-NaOH pH 8.3, 5 mM MgCl2, 10% DMF, 300 mM NaCl, 0.05% Triton-X, 0.01% Digtonin and supplemented with cocktail, 10 mM sodium butyrate), followed by gently flicking and incubating at 37°C for 1 h in the Eppendorf ThermoMixer with 300 rpm. The reaction was gently mixed once after 30 min incubation and stopped by the addition of 10 µl 40 mM EDTA followed by further incubation at 4°C for 10 min. Samples were washed with 0.1% BSA/PBS and finally resuspended in 5 µl Lysis Buffer (0.1 mg/ml Proteinase K, 10 mM Tris-HCl PPH 8.5 and 0.05% SDS) and lysed at 55°C for 3 h in a PCR cycler. 1.8% Triton X-100 with 5 mM PMSF was added to the cell lysate and incubated at RT for 10 min to quench the proteinase K followed by incubation at 55°C for 5 min to quench SDS in the reaction. The DNA can be directly used for PCR amplification by adding 1 µL 25 µM i5 index primer, 1 µL 25 µM i7 index primer, 25 µl 2ⅹKAPA master mix and 17 µL 1 mM MgCl2 to the 6 µL cell lysate for total 50 µl amplification condition. The reaction is set up by incubation at 72°C for 5 min, 98°C for 45 s, 14-18 cycles of (98°C for 15 s, 63°C for 30 s, 72°C for 1 min), and finally 72°C extension for 5 min. After PCR, size selection was carried out by first 0.5ⅹ SPRI beads to remove > 1 kb fragments, and second 0.4ⅹ SPRI beads to the supernatant to obtain 200-1,000 bp fragments for sequencing. The libraries were sequenced with paired-end 150-bp reads on NovaSeq 6000 platform (Illumina).