Translational pauses during a spider fibroin synthesis.

The large ampullate glands of Nephila clavipes synthesize a tissue-specific fibroin for the web and dragline. Its secretory product migrates as one homogeneous band of approximately 320,000 daltons in denaturing electrophoresis. Similar analyses of the secretory epithelium reveal, in addition to the final product, a step ladder array of peptides in a highly reproducible and consistent pattern. We have correlated these peptide ladders with the process of fibroin synthesis. First, the peptides are very prominent in stimulated glands and quite dim in non stimulated ones. Secondly, by offering the cultured glands different amino acids in the incubating medium, we have linked the presence of the bands with those amino acids which abound in the fibroin. The evidence correlates the peptides with active fibroin synthesis, thus they are products of translation, and possibly reflect discontinuities in the translational process such as those demonstrated during the synthesis of Bombyx fibroin.