Fig. 4. Identification of potential protein isoforms of FILIA in mice. (A) Predicted primary structure of 48 kDa (upper) and 38 kDa (lower) isoforms with 440 and 346 amino acids, respectively. N-terminal peptide immunogen common to both isoforms is underlined (black) and regions (amino acids 120-350 and 120-340, respectively) containing a 23 amino acid repeat are indicated by a dashed line (black). Sequences unique to each are bold and italicized. The 50 kDa band (Fig. 2A) containing the presumptive 38 kDa isoform was digested with trypsin and microscale mass spectrometry identified peptides (red) common to both isoforms. (B) FILIA contains a novel, 23 amino acid tandem repeat (120-350 amino acids) defined by RADAR (Heger and Holm, 2000). Amino acids are color-coded: aliphatic, red; uncharged polar, green; acidic, blue; basic, yellow; neutral, magenta. (C) Fluorography of in vitro translation with [³⁵S]methionine of FILIA cDNA encoding the 1.6 (lane 1) and 1.2 (lane 2) kb isoforms of FILIA protein after separation by SDS-PAGE. Molecular masses (kDa) are indicated on the left.