Translation of mRNA for Limulus polyphemus Haemocyanin Polypeptides in vitro: Studies on Subunit Heterogeneity

The haemocyanin of Limulus polyphemus is composed of a munber (possibly 10–15) of polypeptides and is believed to be synthesised in cells called cyanoblasts. In vitro translation in the rabbit reticulocyte heamolysate system and in Xenopusoocytes, of mRNA isolated from cyanoblast-contanining tissue, allowed the detection of several haemocyanin polypeptides amongst the products of translation. At least seven polypeptides with molecular weights in the range 68000–71000 were identified by an immunological method followed by electrophoretic characterisation on two-dimensional polyacrylamide gels. Comparison of the polypeptide patterns of authentic haemocyanin, reticulocyte lysate translation products and Xenopus oocyte translation products led tothe conclusion that the polypeptides are unlikely to undergo significant post-translational modification or to possess cleavable signal sequences. It is proposed that release of haemocyanin into the haemolymph in vivo may involve bursting of the cyanoblasts.