The giant secretory proteins of Chironomus tentans salivary glands: the organization of their primary structure, their amino acid and carbohydrate composition

Abstract

It is generally accepted that the giant secretory proteins of the larval salivary glands of Chironomus tentans are encoded by genes located in Balbiani rings (1 and 2). The major part of the DNA of these genes consists of tandem repeats of 200–240 base pair (bp). It was investigated whether this repetitive sequence arrangement is also expressed at the level of the gene products, the giant secretory proteins (SPs). These proteins were partially digested by an endogenous protease or by papain. It was found that SP Ia and Ib (nomenclature: Rydlander and Edstrom 1980) contain a repetitive primary structure over much of their length. The basic repeat unit is 18,000 daltons. Amino acid analysis of SP I (a+b) revealed a biased distribution which is characteristic for structural proteins. Studies of the carbohydrate composition of SP I (a+b) revealed an unexpectedly high total sugar content of 17.4% (w/w). It was composed of N-acetylglucosamine, glucose, mannose, and galactose in a ratio of 3.4∶6.3∶3.2∶1.0.