Seven Genes of the Enhancer of Split Complex of Drosophila Melanogaster Encode Helix-Loop-Helix Proteins

Enhancer of split [E(spl)] is one of the neurogenic loci of Drosophila and, as such, is required for normal segregation of neural and epidermal cell progenitors. Genetic observations indicate that the E(spl) locus is in fact a gene complex comprising a cluster of related genes and that other genes of the region are also required for normal early neurogenesis. Three of the genes of the complex were known to encode helix-loop-helix (HLH) proteins and to be transcribed in nearly identical patterns. Here, we show that four other genes in the vicinity also encode HLH proteins and, during neuroblast segregation, three of them are expressed in the same pattern. We show by germ-line transformation that these three genes are also necessary to allow epidermal development of the neuroectodermal cells.     

Phenotypic and Molecular Characterization of Ser(d), a Dominant Allele of the Drosophila Gene Serrate

The Drosophila gene Serrate (Ser) encodes a transmembrane protein with 14 epidermal growth factor--like repeats in its extracellular domain, which is required for the control of cell proliferation and pattern formation during wing development. Flies hetero- or homozygous for the dominant mutation Ser(D) exhibit scalloping of the wing margin due to cell death during pupal stages. Ser(D) is associated with an insertion of the transposable element Tirant in the 3' untranslated region of the gene, resulting in the truncation of the Ser RNA, thereby eliminating putative RNA degradation signals located further downstream. This leads to increased stability of Ser RNA and higher levels of Serrate protein. In wing discs of wild-type third instar larvae, the Serrate protein exhibits a complex expression pattern, including a strong stripe dorsal and a weaker stripe ventral to the prospective wing margin. Wing discs of Ser(D) third instar larvae exhibit additional Serrate protein expression in the edge zone of the future wing margin, where it is normally not detectable. In these cells expression of wing margin specific genes, such as cut and wingless, is repressed. By using the yeast Gal4 system to induce locally restricted ectopic expression of Serrate in the edge zone of the prospective wing margin, we can reproduce all aspects of the Ser(D) wing phenotype, that is, repression of wing margin--specific genes, scalloping of the wing margin and enhancement of the Notch haplo-insufficiency wing phenotype. This suggests that expression of the Serrate protein in the cells of the edge zone of the wing margin, where it is normally absent, interferes with the proper development of the margin.     

The linear mitochondrial plasmid pClK1 of the phytopathogenic fungus Claviceps purpurea may code for a DNA polymerase and an RNA polymerase

Summary Plasmid pClK1, a linear mitochondrial plasmid of Claviceps purpurea, was completely sequenced. The sequence contains two long open reading frames (ORF1, 3291 bp; ORF2, 2910 bp), and at least four smaller ORFs. The potential polypeptide derived from ORF1 shows homology to the family B type DNA polymerases. The product of ORF2 has significant homology to the mitochondrial RNA polymerase of yeast and RNA polymerases from bacteriophages. ORF1 and ORF2 show homology to URF3 and URF1 of the maize plasmids S1 and S2, respectively. No homology to any published protein sequence was found for the smaller ORFs. The origin of the terminal protein attached to the 5 ends of pClK1 remains open; several alternatives for its origin are discussed. The sequence data as a whole confirm the virus-like character of pClK1 already postulated from structural properties. Thus pClK1 together with S plasmids of maize and several other linear plasmids make up a distinct class of DNA species of plants and fungi probably derived from a common virus-like ancestor.     

Analysis of nuclear proteins in primary spermatocytes of Drosophila hydei: the correlation of nuclear proteins with the function of the Y chromosomal loops

The protein content of spermatocyte nuclei from X/Y males and mutants of D. hydei which lack different Y chromosomal loop forming sites, was compared with that of X/0 males in ¹⁴C/³H double labelling experiments. Proteins of 45,000, 52,000, 54,000, 66,000, 80,000, 84,000, and 170,000 Dalton are found to be enriched in nuclei containing two or more active Y chromosomal loop forming sites. These proteins are also present in the nuclei of X0 males. In the complete absence of the Y-chromosomal loops proteins of 35,000, 46,000, 58,000 and 110,000 Dalton become enriched in the spermatocyte nuclei. — Analysis of the nuclear RNP of spermatocytes led to the isolation of an hnRNP-containing fraction with an S-value of >900S (RNP-PP). — In the RNP-PP of XY males labelled protein material associated with hnRNA is enriched by a factor of 3 in respect to the X0 genotype. The nuclear RNP has a heterogenous buoyant density in CsCl of p = 1.33 to 1.43 g/cm³. RNase T₁ treatment of the crude nuclear RNP from XY males prior to sucrose gradient analysis shows that the 66,000 Dalton protein which is also strongly enriched in the nuclei in the presence of active Y chromosomal loop forming sites, is the main protein associated with protected RNA-sequences of 80–120 and 200–300 nucleotides in length. Competitive nitrocellulose filter binding assays reveal that the 66,000 Dalton protein predominantly forms in 2 M NaCl stable RNA/protein complexes with the poly A ⁺hnRNA of the RNP-PP. These RNP complexes have a buoyant density of p = 1.43 g/cm³ in CsCl. The results are discussed in relation to the nuclear structure and the function of the Y chromosomal loops during spermatogenesis in Drosophila hydei.