Larval salivary gland secretion proteins in Drosophila structural analysis of the Sgs-5 gene

The structure of the Drosophila melanogaster salivary gland secretion gene Sgs-5 has been determined by DNA sequence analysis of cloned genomic DNA. This developmentally and tissue-specific gene is a member of the third instar intermolt gene set and is under control of the insect molting hormone ecdysterone. RNA protection experiments show that the RNA coding region of Sgs-5 contains 769 nucleotides and is divided into three exons by two small introns. The protein-coding region appears to begin after a short untranslated RNA leader (33 nucleotides) and to result in a protein of 163 amino acids. The first 18 amino acids give the amino-terminal end the highly hydrophobic nature characteristic of a signal peptide.     

The normal developmental regulation of a cloned sgs3 ''glue'' gene chromosomally integrated in Drosophila melanogaster by P element transformation.

A 7-kb genomic segment containing the coding sequence for the Drosophila melanogaster Formosa variant of salivary gland secretion protein 3 (sgs3) has been inserted into the snw y, bw, st strain of D. melanogaster using the P transformation vector p.6.1. The inserted sequence codes for a shorter RNA which can be distinguished from that of the host gene. The amount of RNA, and its stage- and tissue-specific synthesis is identical to that of the host gene, which suggests that all the cis-acting regulatory DNA sequences for this gene are contained within this 7-kb segment.     

Drosophila: the genetics of two major larval proteins.

A series of irradiation-induced deficiencies covering 62 polytene chromosome bands in chromosome arm 3L of Drosophila melanogaster includes the loci of two abundant developmentally regulated larval proteins. The structural gene for larval serum protein 2 (LSP 2) lies at 68E3 or 4, and that for salivary glue secretion protein 3 between 68A8 and 68C11, coincident with a major intermoult puff active in the salivary gland at the time of glue synthesis. The structural genes for esterase 6 and four visible recessive loci lie within the same region.     

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

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.     

Primary sequence and developmental expression of a novel Drosophila melanogaster src gene.

We have sequenced a cDNA clone for the Drosophila melanogaster gene Dsrc28C, a homolog of the vertebrate gene c-src. The cDNA contains a single open reading frame encoding a protein of 66 kilodaltons which contains features highly conserved within the src family of tyrosine protein kinases. Novel structural features of the Dsrc28C protein include a basic pI and a polyglycine domain near the amino terminus. Cell-free translation of in vitro-transcribed RNA yielded a protein of the predicted size which could be immunoprecipitated by anti-v-src antisera. RNA blot hybridization revealed that the gene is expressed predominantly during embryogenesis, in imaginal disks of third-instar larvae, and in adult females. In situ hybridization showed that expression in adult females is largely confined to nurse cells and developing oocytes.     

Thermal compensation in protein and RNA synthesis during the intermolt cycle of the American lobster, Homarus americanus.

1. The in vitro rates of incorporation of precursors into protein and RNA and the concentration of RNA were measured in tissues of intermolt and premolt lobsters acclimated to 5 degrees C and 20 degrees C. Midgut gland, abdominal muscle and gill of intermolt lobsters respond to temperature acclimation by a compensatory translation of the rate-temperature (R-T) curves with respect to the rates of incorporation of 3H-leucine and 3H-uridine into the acid-insoluble fraction. Midgut gland and muscle of premolt animals exhibit either no compensation or inverse compensation; gill tissue exhibits a rotation of the R-T curve. 2. The existence of the complete de novo pathway of pyrimidine biosynthesis is demonstrated in the class Crustacea. NaH14 CO2 is incorporated into orotic acid and orotic-14 C-acid is incorporated into the acid-insoluble fraction. 3. Both the concentration of RNA and the rates of incorporation of precursors of both the salvage and de novo pyrimidine pathways are enhanced in the midgut gland of premolt lobsters, relative to intermolt tissue, under conditions of warm-acclimation.     

Polarized secretion of an ectopic protein in Drosophila salivary glands in vivo.

Epithelial cells can secrete specific proteins in a polarized manner, either from the apical or basolateral surface. Intracellular protein sorting which results in polarized secretion has previously been studied using epithelial tissue culture cells. We describe here the use of Drosophila larval salivary glands for the study of polarized secretion by epithelia in vivo, and address whether an ectopically synthesized secretory protein can be sorted and targeted to the correct cell surface for secretion. Larval cuticle proteins (LCPs) and salivary gland secretion (Sgs) proteins of Drosophila melanogaster are apically secreted proteins that are produced respectively by the epidermis and salivary glands. We have transformed Drosophila with a hybrid gene consisting of the sgs-4 promoter sequence and the coding sequence for a variant (LCP-f2) of LCP-2. We have found that transgenic late third instar larvae produce LCP-f2 only in the salivary glands and that LCP-f2 is properly secreted in vivo in a polarized manner from only the apical surface of the cells into the gland lumen. The results indicate that apical secretion does not depend on a tissue-specific targeting signal contained within the protein.     

Isolation and characterization of cloned DNA sequences containing ribosomal protein genes of Drosophila melanogaster.

Ribosomal (r) proteins encoded by polyadenylated RNA were specifically precipitated in vitro from polysomes by using antibodies raised against characterized Drosophila melanogaster r proteins. The immuno-purified mRNA in the polysome complex was used to prepare cDNA with which to probe a D. melanogaster genomic library. Selected recombinant phages were used to hybrid select mRNAs, which were analyzed by in vitro translation. Three clones containing the genes for r proteins 7/8, S18, and L12 were positively identified by electrophoresis of the translation products in one-dimensional and two-dimensional polyacrylamide gels. Sequences encoding r proteins S18 and L12 were found to be present in the genome in single copies. In contrast, the polynucleotide containing the region encoding 7/8 may be repeated or may contain or be flanked by short repeated sequences. The sizes of mRNAs that hybridized to the recombinant clone containing 7/8 were significantly larger than would be expected from the molecular weight of protein 7/8, implying that there were unusually long 5' and 3' noncoding sequences. The mRNAs for r proteins S18 and L12 were however, only about 10% larger. In situ hybridizations to salivary gland polytene chromosomes, using the recombinant phage, revealed that the recombinant clone containing the gene for r protein 7/8 hybridized to 5D on the X chromosome; the recombinant clone containing the gene for S18 hybridized to 15B on the same chromosome, and the recombinant phage containing the gene for L12 hybridized to 62E on chromosome 3L. It is of interest that the genomic locations of all three r protein clones were within the chromosomal intervals known to contain the Minute mutations [M(1)0, M(1)30, and M(3)LS2]. Although each clone contained sequences specifying two to four proteins, none had more than one identifiable r protein gene, suggesting that different D. melanogaster r protein genes may not be closely linked.     

Cell-free translation of proline-rich protein mRNAS from human submandibular gland

RNA was isolated from a human submandibular gland and separated into poly A-enriched and poly A-deficient fractions by chromatography on oligo (dT) cellulose. Both of these RNA fractions stimulated methionine incorporation into polypeptides in a reticulocyte lysate translation system. Two in vitro translation products templated by poly A-enriched mRNA were isolated by immunoprecipitation with immune serum directed against human salivary anionic proline-rich protein I. These polypeptides were shown to be precursors of proline-rich proteins on the basis of Mr, affinity for the antiserum, and preferential incorporation of proline. This study is the first to demonstrate cell-free translation of the mRNAs for human proline-rich salivary protein precursors.     

Differential distribution of RNA polymerase B and nonhistone chromosomal proteins in polytene chromosomes of Drosophila melanogaster

The distribution patterns of nonhistone chromosomal proteins (NHCP) associated with pulse-labeled RNA were determined by indirect immunofluorescence on salivary gland chromosomes of Drosophila melanogaster using monoclonal antibodies. By staining for two different antigens simultaneously, using antibodies tagged with different fluorescent probes, it became possible to position RNA-associated antigens as well as RNA polymerase B in relation to each other. Three separate staining patterns could be observed with anti-NHCP antibodies, none of which showed a pattern which was identical with that of RNA polymerase B. Furthermore, no correlation with the synthesis of the primary trancript, as monitored by the RNA polymerase B content of chromosomal sites, could be found by following the fluorescence patterns during inactivation of intermolt puffs or activation of early ecdysone-induced puffs. Finally, no strict correlation was observed between puffing activity and the accumulation of a certain antigen in these selected chromosomal sites.     

Translational Control of UIS4 Protein of the Host-Parasite Interface Is Mediated by the RNA Binding Protein Puf2 in Plasmodium berghei Sporozoites

UIS4 is a key protein component of the host-parasite interface in the liver stage of the rodent malaria parasite Plasmodium berghei and required for parasite survival after invasion. In the infectious sporozoite, UIS4 protein has variably been shown to be translated but also been reported to be translationally repressed. Here we show that uis4 mRNA translation is regulated by the P. berghei RNA binding protein Pumilio-2 (PbPuf2 or Puf2 from here on forward) in infectious salivary gland sporozoites in the mosquito vector. Using RNA immunoprecipitation we show that uis4 mRNA is bound by Puf2 in salivary gland sporozoites. In the absence of Puf2, uis4 mRNA translation is de-regulated and UIS4 protein expression upregulated in salivary gland sporozoites. Here, using RNA immunoprecipitation, we reveal the first Puf2-regulated mRNA in this parasite.     

A salivary gland-specific, maltase-like gene of the vector mosquito, Aedes aegypti

Genomic and cDNA clones of a gene expressed specifically in the salivary glands of adult Aedes aegypti have been isolated and sequenced. This gene encodes an abundant mRNA that is transcribed throughout the male salivary gland but only in the cells of the proximal lateral lobes of the female gland. The deduced protein has many basic amino acids, several possible sites for N-glycosylation, and displays striking similarities with the products of a yeast maltase gene and three previously unidentified genes from Drosophila melanogaster. We propose the name 'Maltase-like I' (MalI) to designate this gene. The presumed function of this gene product is to assist the mosquito in its sugar-feeding capabilities. The mosquito and fruitfly genes have similar structural features 5' to the protein coding regions, indicating that these genes may share common control mechanisms.     

AP-1 and clathrin are essential for secretory granule biogenesis in Drosophila

Regulated secretion of hormones, digestive enzymes, and other biologically active molecules requires the formation of secretory granules. Clathrin and the clathrin adaptor protein complex 1 (AP-1) are necessary for maturation of exocrine, endocrine, and neuroendocrine secretory granules. However, the initial steps of secretory granule biogenesis are only minimally understood. Powerful genetic approaches available in the fruit fly Drosophila melanogaster were used to investigate the molecular pathway for biogenesis of the mucin-containing "glue granules" that form within epithelial cells of the third-instar larval salivary gland. Clathrin and AP-1 colocalize at the trans-Golgi network (TGN) and clathrin recruitment requires AP-1. Furthermore, clathrin and AP-1 colocalize with secretory cargo at the TGN and on immature granules. Finally, loss of clathrin or AP-1 leads to a profound block in secretory granule formation. These findings establish a novel role for AP-1- and clathrin-dependent trafficking in the biogenesis of mucin-containing secretory granules.