Serine-38 of Ana2 is phosphorylated in vitro by Plk4 as identified by mass-spectrometry. from Two-step phosphorylation of Ana2 by Plk4 is required for the sequential loading of Ana2 and Sas6 to initiate procentriole formation S. DzhindzhevNikola TzolovskyGeorge LipinszkiZoltan AbdelazizMohammed DebskiJanus DadlezMichal GloverDavid M. 2017 Supplementary Figure S2. Serine-38 of Ana2 is phosphorylated in vitro by Plk4 as identified by mass-spectrometry. Phospho-Mascot-interpreted fragmentation spectra of the peptide 13-LAPRP…EV (phospho-S-38) ILFG…SPR-65 with phosphorylated serine at the position 38 (highlighted red). Labelled peaks correspond to fragment ions. Despite the relatively long peptide, the fragmentation pattern unambiguously identifies the phosphorylation site.