Still, both S149 and S153 are immediately succeeded by a proline (P), which is significant as proteins phosphorylated on serine or threonine immediately preceding proline are known to play essential roles in the regulation of cellular processes . Additional significance to the inability of BPF to successfully determine the exact location of protein phosphorylation within this region is due to the fact that this phosphorylation is detected near the SST motif contained within D155-G159. This is a highly conserved region demonstrated to be essential for AAV transduction efficiency, with phosphomimetic replacements shown to negatively impact virus formation and transduction .