title: Z4_1ng_small_1
design: Total RNA was extracted from approximately one million mESCs using                 an RNeasy Plus Mini kit (QIAGEN), 1ng diluted total RNA was mixed with with 100 ng                 small carrier RNA. The small RNA sequencing library was constructed following the                 manufacturer's protocol using a NEBNext kit (NEB #E7300). After PCR amplification                 (15 cycles), the cDNA fragment from the RNA carrier was removed by Not I digestion.                 After Not I digestion, the library DNA was purified for deep                 sequencing.