A single stranded DNA binding protein was received from ----someone with
the request to identify the species of origin. The protein was denatured
with 2M guanidine HCl (pH 8), reduced with 10 mM dithiothreitol at 65
oC for 1 h and alkylated with 50 mM iodoacetamide in the dark for 45
min at room temperature. Trypsin was added to the protein sample at an
enzyme-to-protein ratio of 1:20 (w/w), and digestion was carried out for
17 h at 37 oC.  Total reaction volume was 50 uL. The digestion reaction
was quenched by acidification with 0.5 uL of glacial acetic acid. The
peptides were analyzed by liquid chromatography-tandem mass spectrometry
(LC-MS/MS) using an LTQ Orbitrap XL mass spectrometer. Peptides were
separated on a C18 column using a gradient of 0.1% formic acid in
water with increasing acetonitrile (up to 40%, also modified with
formic acid). Mass spectrometry data were acquired in positive ion
mode with an m/z range of 350-2000. Search databases were as described
in the figures.  In all cases, searches were performed by FragPipe
(https://fragpipe.nesvilab.org/, 20 ppm tolerance of parent ion, 2 missed
cleavages) after the addition of decoys and common contaminants.