Isolation and structural analysis of a ribosomal protein gene in D.melanogaster

Mutation in P0, a dual function ribosomal protein/apurinic/apyrimidinic endonuclease, modifies gene expression and position effect variegation in Drosophila

In a search for modifiers of gene expression with the white eye color gene as a target, a third chromosomal P-element insertion mutant l(3)01544 has been identified that exhibits a strong pigment increase in a white-apricot background. Molecular analysis shows that the P-element insertion is found in the first intron of the gene surrounding the insertion site. Sequencing both the cDNA and genomic fragments revealed that the identified gene is identical to one encoding ribosomal protein P0/apurinic/apyrimidinic endonuclease. The P-element-induced mutation, l(3)01544, affects the steady-state level of white transcripts and transcripts of some other genes. In addition, l(3)01544 suppresses the variegated phenotypes of In(1)wm4h and In(1)y3P, suggesting a potential involvement of the P0 protein in modifying position effect variegation. The revertant generated by the precise excision of the P element has lost all mutant phenotypes. Recent work revealed that Drosophila ribosomal protein P0 contains an apurinic/apyrimidinic endonuclease activity. Our results suggest that this multifunctional protein is also involved in regulation of gene expression in Drosophila.

The Drosophila melanogaster lipase homologs: a gene family with tissue and developmental specific expression

We report the molecular cloning of Drosophila genes encoding putative lipase homologs, Dm lip1, lip2 and lip3, the definition of their structure and the expression patterns during development. These Drosophila lipases are related to acid lipases, with a common GHSQG motif, within a more general consensus GXSXG, identified as the active site shared by all the members of lipase superfamily. The lip1 and lip3 genes are transcribed in different tissues and developmental stages, suggesting that they have different functions. The lip1 gene, coding for a protein similar to digestive lipases, is expressed in ovaries and early embryos and, with a different sized transcript, in all the other developmental stages. The lip3 gene, whose translation product is more similar to lysosomal acid lipases, is expressed only during the larval period. The lip2 gene seems non-functional. The Drosophila putative lipases do not show similarity with the Drosophila yolk proteins that are reported to have sequence similarity with lipoprotein lipases, but share a consistent similarity with lepidopteran proteins reported as egg specific or yolk proteins, probably corresponding to lipase homologs. The results reported here are discussed in relation to the evolution and functions of lipases within the between species.

Expression of Drosophila melanogaster F elements in vivo

Drosophila melanogaster F elements are mobile, oligo(A)-terminated DNA sequences that probably propagate by the retrotranscription of RNA intermediates. Polyadenylated transcripts corresponding in size to full-length (4.7 kb) family members were detected in the Drosophila melanogaster Canton-S strain from 2nd larval instar to the adult stage. RNA accumulation reached a maximum in pupae. In the adult, F elements are transcribed in both sexes. F expression is directed in vivo by the intragenic promoter (Fin) located at the 5' end of F. Whole-mount hybridizations were carried out to define the site of synthesis of full-length transcripts found in the ovary. Selective RNA accumulation was not detected in the cytoplasm of any specific cell type. Stained nuclear dots were observed in nurse cells from stage 2-3 to the end of oogenesis. RNase treatment of egg chambers prior to the addition of the probe led to disappearance of the nuclear dots and appearance of a cytoplasmic hybridization signal suggesting leakage of nuclear transcripts. Transgenic lines harbouring the chloramphenicol acetyltransferase (CAT) gene under the control of the Fin promoter were obtained. In independent lines, CAT enzyme levels mirror the ontogenetic profile of F expression drawn from Northern RNA blotting data. An antisense promoter (Fout) that is located downstream from the Fin promoter and transcribe too bords the 5' end of F seems to be constitutively expressed in the fly.

Drosophila ribosomal protein L18a: cDNA sequence, expression and chromosomal localization of the gene

We describe the cDNA sequence of the Drosophila homologue of the rat ribosomal protein L18a. The protein sequence predicted has identical or conservatively substituted amino acids in 80% of positions. It is distinctly basic in character with an overall net positive charge of + 20. Analysis of L18a RNA with the Northern blot technique shows it to be expressed both during embryonic development and in the adult fly. In situ hybridisation to polytene chromosomes reveals that the L18a gene(s) is located at 54B on the second chromosome.

A Drosophila third chromosome Minute locus encodes a ribosomal protein

Minutes (M) are a group of over 50 phenotypically similar Drosophila mutations widely believed to affect ribosomal protein genes. This report describes the characterization of the P element-induced M(3)95A(Plac92) mutation [allelic to M(3)95A]. This mutation can be reversed by the mobilization of the P element, demonstrating that the mutation is caused by insertion of this transposable element. The gene interrupted by insertion of the P element was cloned by use of inverse polymerase chain reaction. Nucleotide sequence analysis revealed a 70-75% identity to the human and rat ribosomal protein S3 genes, and to the Xenopus ribosomal protein S1a gene. At the amino acid level, the overall identity is approximately 78% for all three species. This is only the second time that a Minute has been demonstrated to encode a ribosomal protein.

Sequence and expression of a gene encoding a ribosomal protein S4 homolog from Drosophila melanogaster

We describe a Drosophila melanogaster cDNA clone encoding an amino acid (aa) sequence 75% identical to human ribosomal protein S4 (RPS4). The D. melanogaster RPS4 has 260 aa, if the NH2-terminal methionine is removed after translation of the mRNA. The mRNA for the protein is about 1 kb in length and is detected throughout the developmental stages tested (i.e., embryo, larva, pupa and adult). The cDNA clone hybridizes to two sites on the X chromosome, 1B1-2 and 3A3-6.

Ribosomal protein S14 is not responsible for the Minute phenotype associated with the M(1)7C locus in Drosophila melanogaster

A locus associated with a severe Minute effect has been mapped at 7C on the X chromosome of Drosophila melanogaster. Previous work has suggested that this Minute encodes ribosomal proteins S14A and S14B. We have made a chromosomal deficiency that removes the S14 ribosomal protein genes, yet does not display the Minute phenotype. These data suggest that the S14 genes do not actually correspond to the Minute locus.

The l(3)S12 locus of Drosophila melanogaster: heterochromatic position effects and stage-specific misexpression of the gene in P element transposons

l(3)S12 is a vital locus whose function is required in embryos, early larvae, late pupae and oogenesis. We have identified a cold-sensitive allele, l(3)S12(3), and characterized conditional misexpression of the gene associated with this mutation as well as with several euchromatic insertions of l(3)S12+ transposons. Surviving cold-sensitive mutants as well as underexpression variants generated by P element transformation display a phenotypic syndrome that can include delayed development, abnormal bristle morphology, and female sterility. Using these phenotypes, defects in putative "early" and "late" l(3)S12 expression can be identified. The sensitivity of certain l(3)S12+ insertions to site-specific euchromatic position effect appears to be due to separation of the gene from an endogenous enhancer element during cloning. This enhancerless construct can be used to identify and perhaps to select "permissive" euchromatic sites, presumably adjacent to enhancer elements, which in some cases permit elevated production not only of the l(3)S12 message, but also of a P element-l(3)S12 fusion transcript. Certain of these permissive sites appear to control stage-specific expression, and we propose that this system may be used to identify, clone, and characterize such loci. Heterochromatic position effect on this locus has been demonstrated. Available evidence suggests that the l(3)S12 gene may be involved in protein synthesis, perhaps encoding a ribosomal protein.

A small gene family in barley encodes ribosomal proteins homologous to yeast YL17 and L22 from archaebacteria, eubacteria, and chloroplasts

The amino acid sequences of two barley ribosomal proteins, termed HvL17-1 and HvL17-2, were decoded from green leaf cDNA clones. The N-terminal sequences of the derived barley proteins are 48% identical to the N-terminal amino acid sequence of protein YL17 from the large subunit of yeast cytoplasmic ribosomes. Via archaebacterial ribosomal proteins this homology extends to ribosomal protein L22 from eubacteria and chloroplast. Barley L17, and ribosomal proteins L22 and L23 from the archaebacteria Halobacterium halobium and H. marismortui, are 25-33% identical. Interestingly, the barley and archaebacterial proteins share a long, central stretch of amino acids, which is absent in the corresponding proteins from eubacteria and chloroplasts. Barley L17 proteins are encoded by a small gene family with probably only two members, represented by the cDNA clones encoding HvL17-1 and HvL17-2. Both these genes are active in green leaf cells. The expression of the L17 genes in different parts of the 7-day old barley seedlings was analyzed by semiquantitative hybridization. The level of L17 mRNA is high in meristematic and young cells found in the leaf base and root tip. In the leaf, the L17 mRNA level rapidly decreases with increasing cell age, and in older root cells this mRNA is undetectable.

The 5' splice site: phylogenetic evolution and variable geometry of association with U1RNA

The 5' splice site sequences of 3294 introns from various organisms (1-672) were analyzed in order to determine the rules governing evolution of this sequence, which may shed light on the mechanism of cleavage at the exon-intron junction. The data indicate that, currently, in all organisms, a common sequence 1GUAAG6U and its derivatives are used as well as an additional sequence and its derivatives, which differ in metazoa (G/1GUgAG6U), lower eucaryotes (1GUAxG6U) and higher plants (AG/1GU3A). They all partly resemble the prototype sequence AG/1GUAAG6U whose 8 contigous nucleotides are complementary to the nucleotides 4-11 of U1RNA, which are perfectly conserved in the course of phylogenetic evolution. Detailed examination of the data shows that U1RNA can recognize different parts of 5' splice sites. As a rule, either prototype nucleotides at position -2 and -1 or at positions 4, 5 or 6 or at positions 3-4 are dispensable provided that the stability of the U1RNA-5' splice site hybrid is conserved. On the basis of frequency of sequences, the optimal size of the hybridizable region is 5-7 nucleotides. Thus, the cleavage at the exon-intron junction seems to imply, first, that the 5' splice site is recognized by U1RNA according to a "variable geometry" program; second, that the precise cleavage site is determined by the conserved sequence of U1RNA since it occurs exactly opposite to the junction between nucleotides C9 and C10 of U1RNA. The variable geometry of the U1RNA-5' splice site association provides flexibility to the system and allows diversification in the course of phylogenetic evolution.