The structural genes for three Drosophila glue proteins reside at a single polytene chromosome puff locus.

Abstract

The polytene chromosome puff at 68C on the Drosophila melanogaster third chromosome is thought from genetic experiments to contain the structural gene for one of the secreted salivary gland glue polypeptides, sgs-3. Previous work has demonstrated that the DNA included in this puff contains sequences that are transcribed to give three different polyadenylated RNAs that are abundant in third-larval-instar salivary glands. These have been called the group II, group III, and group IV RNAs. In the experiments reported here, we used the nucleotide sequence of the DNA coding for these RNAs to predict some of the physical and chemical properties expected of their protein products, including molecular weight, amino acid composition, and amino acid sequence. Salivary gland polypeptides with molecular weights similar to those expected for the 68C RNA translation products, and with the expected degree of incorporation of different radioactive amino acids, were purified. These proteins were shown by amino acid sequencing to correspond to the protein products of the 68C RNAs. It was further shown that each of these proteins is a part of the secreted salivary gland glue: the group IV RNA codes for the previously described sgs-3, whereas the group II and III RNAs code for the newly identified glue polypeptides sgs-8 and sgs-7.Drosophila melanogaster begins life as a fertilized egg, which after a day of embryonic development hatches as a wormlike first-instar larva. After another day this larva molts and becomes a larger, second-instar larva; one further day leads to a second molt and the last stage of larval life, the third larval instar. This lasts two days, at the end of which the larval cuticle hardens to form a pupal case. After an immobile prepupal period, pupation and metamorphosis occur, resulting in an adult fly. The major synthetic activity of the salivary gland cells of the third-instar larva is the production of a set of about 10 polypeptides that are secreted into the lumen of the gland after synthesis and that at the end of larval life are expelled through the duct of the salivary glands and deposited on the surface upon which the larva rests. This protein secretion serves as a glue that causes the prepupa, and subsequently the pupa, to adhere to its substrate for the duration of the pupal period (5,8,15,16

The 68C Glue Puff of Drosophila

“…The RNAs are all polyadenylated and polysomal (Meyerowitz and Hogness 1982). By comparing conceptual translations of the eDNA sequences with partial amino acid sequences of different glue polypeptides, it was found that each of the 68C RNAs codes for a different glue component (Crowley et al 1983). The 1120-nucleotide RNA is the mRNA for the sgs-3 glue polypeptide, which had previously been shown by genetic mapping to be coded in or near the 68C puff (Korge 1975;Akam et al 1978).…”

“…Both genetic and molecular experiments have shown that these puffs contain the structural genes for the polypeptides that comprise the salivary gland glue (Korge 1975(Korge , 1977Akam et al 1978;Muskavitch and Hogness 1980;Velissariou andAshburner 1980, 1981;Crowley et al 1983;Gautam 1983;Guild and Shore 1984). This glue consists of at least eight polypeptides that start to be synthesized in the salivary glands in early to midthird instar, and stop synthesis at the time of puparium formation (Beckendorf and Kafatos 1976).…”

Characterization of the boundaries between adjacent rapidly and slowly evolving genomic regions in Drosophila.

“…stays nearly constant, The 68C puff of Drosophila melanogaster contains three genes that code for components of a protein glue that affixes the puparial case to a solid substrate (1)(2)(3). These genes are expressed abundantly in the salivary glands of third instar larvae and are controlled by the steroid hormone ecdysterone (4-7).…”

cis-acting sequences required for expression of the divergently transcribed Drosophila melanogaster Sgs-7 and Sgs-8 glue protein genes.

“…As enzyme activity produced by fusion This observation is consistent with the kinds of fusion genes used. Sgs-7-Adh is a transcriptional fusion in the 5' untranslated leader of both genes and therefore produces native ADH protein that lacks a signal peptide for transport into the lumen (9). In contrast, Sgs-8-lacZ is a translational fusion with the coding sequences for 51 amino acids from Sgs-8 present and contains the signal peptide necessary for secretion into the lumen of the gland.…”