## 3 Results
### In Silico Analysis of RNA Binding Proteins (RBPs)  
To find potential binding proteins to the pri-miR-125a containing C- and U-variants, we analyzed the 51-nucleotide fragment of pri-miR-125a using RBPmap web server and ATtRACT database [27; 28]. Both, the C- and U-variants were analyzed using RBPmap with three different stringency levels: low, medium, and high. Low stringency level corresponds to significant \(p\)-value \(<\) 0.01 and suboptimal \(p\)-value \(<\) 0.02; medium stringency level thresholds were at significant \(p\)-value \(<\) 0.005 and suboptimal \(p\)-value \(<\) 0.01; high stringency level was set to \(<\)0.001 and \(<\)0.01 for significant \(p\)-value and suboptimal \(p\)-value, respectively. We searched for any available human motif stored in RBPmap. Low stringency algorithm mapped SRSF5, PTBP1, and PCBP1 proteins in both C-/U-variants. BRUNOL4 and BRUNOL5 proteins were only mapped in U-variant, whereas SRSF3, HNRNPK, and NOVA1 proteins were only \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Recceptor**} & \multirow{2}{*}{**Case**} & \multirow{2}{*}{**Variant**} & \multicolumn{2}{c}{**Group Status**} & \multirow{2}{*}{\(p\)**-Value**} \\ \cline{3-4} \cline{6-6}  & & & **P** & **N** & \\ \hline \multirow{4}{*}{HER2} & \multirow{4}{*}{Genotype} & TT & 14 & 30 & \\ \cline{3-4} \cline{6-6}  & & CT & 7 & 48 & \\ \cline{3-4} \cline{6-6}  & & CC & 1 & 6 & \\ \cline{3-4} \cline{6-6}  & & TT+CT & 21 & 78 & \\ \cline{3-4} \cline{6-6}  & & CT+CC & 8 & 54 & \\ \cline{3-4} \cline{6-6}  & & T & 35 & 108 & \\ \cline{3-4} \cline{6-6}  & & C & 9 & 60 & \\ \hline \multirow{4}{*}{ER} & \multirow{4}{*}{Genotype} & TT & 36 & 8 & \\ \cline{3-4} \cline{6-6}  & & CT & 37 & 17 & \\ \cline{3-4} \cline{6-6}  & & CC & 6 & 1 & \\ \cline{3-4} \cline{6-6}  & & TT+CT & 73 & 25 & \\ \cline{3-4} \cline{6-6}  & & CT+CC & 33 & 18 & \\ \cline{3-4} \cline{6-6}  & & T & 109 & 33 & \\ \cline{3-4} \cline{6-6}  & & C & 49 & 19 & \\ \hline \multirow{4}{*}{PR} & \multirow{4}{*}{Genotype} & TT & 30 & 14 & \\ \cline{3-4} \cline{6-6}  & & CT & 35 & 20 & \\ \cline{3-4} \cline{6-6}  & & CC & 6 & 1 & \\ \cline{3-4} \cline{6-6}  & & TT+CT & 65 & 34 & \\ \cline{3-4} \cline{6-6}  & & CT+CC & 41 & 21 & \\ \cline{3-4} \cline{6-6}  & & T & 95 & 48 & \\ \cline{3-4} \cline{6-6}  & & C & 47 & 22 & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The association analysis between miR-125a rs12976445 polymorphism and HER2, ER and PR receptors status in breast cancer patients. The association was calculated using \(\chi\) square test. The status of receptors was divided into two groups-positive (P) and negative (N). found in C-variant. In medium and high stringency levels, RBPmap found only PTBP1 protein motif in U-variant. For the C-variant, medium stringency algorithm found following potentially binding proteins: SRSF3, HNRNRPK, NOVA1, and PTBP1. High stringency level for C-variant found the same RBPs as the medium algorithm, excluding HNRNRPK protein. All RBPmap-predicted proteins that potentially bind to the region containing C-/U-variant in 51-miR-125a sequence are shown in Table 3.  
We focused on proteins that were variant-specific. Less frequent C-variant interacts potentially with HNRNPK and NOVA1--the proteins involved in the RNA processing [35; 36]. The C-variant was also mapped with SRSF3 protein, which was not found by RBPmap in U-variant on any stringency level of the algorithm execution and appeared on every stringency level of C-variant. On the contrary, BRUNOL4 and BRUNOL5, proteins that regulate alternative splicing of pre-mRNA and are possibly connected with mRNA editing and translation, were only mapped in U-variant of the analyzed sequence. In the next step, we used ATtRACT database to search for potential RBP motifs in 51-miR-125a sequence. In the U-variant, ATtRACT predicted PTBP1 motif corresponding to the results from RBPmap, where PTBP1 was mapped in all three stringency levels of the algorithm. In the C-variant, ATtRACT predicted YBX1 and NOVA1 binding motifs.