Mapping of translation initiation of ERG isoforms.

<p>(<b>A</b>) N-terminal heterogeneity in human native ERG variants. The 5′ regions for the indicated variants are reproduced. Boxes represent exons with the ORF in blue. Red ticks below the exons indicate in-frame ATGs in exons 1c and exons 3 to 5. The out-of-frame products caused by exon skipping, from the otherwise in frame ATGs are indicated in red. (<b>B</b>) Western Blot (WB) of transient expression of the variants in HeLa cells. Antibody C20 recognizes exogenous protein and an endogenous band at ∼44 KDa corresponding in size to Δ4 variants. Antibody C17 preferentially recognizes exogenous ERG bands. (<b>C</b>) Mutations that independently eliminate the 3 in-frame ATGs in exon 4 were introduced into the cDNA of T1:E4 and analyzed as above. (<b>D</b>), Similarly, mutations were introduced to eliminate the ATGs in exon 3 (ERG-1b) or in exon 1c (ERG-1c) by themselves or in combination with mutations in the first in-frame ATG (M4a) in exon 4 (ERG-1b and ERG-1c).