Mutations in the ATG site normally used as start of translation and other mutations, as indicated by the red X, result in the production of N-terminally truncated elastase lacking the signal peptide (red bars). These truncated proteins are liberated to the cytosol instead of being routed to the endoplasmic reticulum and granules as is wild-type elastase (black bar). See Figure 6 in the article by Tidwell et al that begins on page 562. ER, endoplasmic.