title: 553
design: Libraries for deep sequencing were prepared according to the manufacturer*s protocol (SREK [small RNA expression Kit], Applied Biosystems, Foster City, USA). After cDNA preparation, the library was amplified using an in-gel procedure. In brief, RNaseH-treated cDNA was purified using MinElute columns (QIAGEN). After separating the eluate on a 6 % PAGE, the 60 – 90 bp section was excised from the gel and the pieces were subjected to 18 cycles of large scale PCRProP with barcoded primers included in the SREK kit. Products were purified on MinElute Columns and resolved on a 6 % TBE PAGE. The 105-150 bp fraction was incubated overnight in PAGE Elution buffer (Applied Biosystems) and integrity of the library was checked using the DNA 1000 Lab Chip on a Bioanalyzer Device (Agilent, Santa Clara, CA). Template bead preparation, emulsion PCR and deposition was performed according to the standard protocol and slides were analyzed on a SOLiD system V3 (Applied Biosystems).