Roland Rosset

Effects of ecdysone on a Drosophila cell line.

Abstract When treated by ecdysone, Drosophila cells of the line Kc start aggregating in clumps 24 h later. Different early events occur before this morphological process: DNA synthesis and mitosis stop after 8–10 h; RNA synthesis after a transient stimulation is progressively inhibited.

Mutations in ccf, a novel Drosophila gene encoding a chromosomal factor, affect progression through mitosis and interact with Pc‐G mutations

We report herein the isolation of ccf, a new gene located in region 82E and essential for Drosophila development. This gene, expressed throughout development, encodes a novel product of 68 kDa which is found in the nucleus during interphase and labels, in a novel pattern, centrosomes and chromosome arms during mitosis. Mutations in ccf give rise to late larvae with small imaginal discs and to adults showing appendages of reduced size, consistent with CCF involvement in cell proliferation. Neuroblast squash analyses show that CCF is required for proper condensation of mitotic chromosomes and, therefore, for progression through mitosis. Furthermore, we observe that adult ccf mutants as well as animals overexpressing CCF during larval stages exhibit homeotic transformations. We also find that mutations in the Pc‐G genes Polycomb, polyhomeotic and Enhancer of zeste are enhanced by ccf mutations. Finally, we show that the CCF protein binds to specific sites on polytene chromosomes, many of which are shared with the Posterior sex combs Pc‐G protein. Together, these results suggest a role for the CCF protein in the maintenance of chromosome structure during mitosis and interphase.

Properties of ribosomes from erythromycin resistant mutants of Escherichia coli.

SummaryWe have studied the in vitro properties of ribosomes from several mutants resistant to erythromycin. Mutations in three different genes may confer resistance to erythromycin. Two of them are structural genes for proteins L4 and L22 of the large subunit. The third mutation (in eryC gene) seems to affect mainly the small subunit. The mechanism of action of the antibiotic may involve both subunits.

Heterogeneity of 5S RNA in Escherichia coli

SummaryFrom finger-print analysis of 5S RNA isolated from 4 different Escherichia coli strains, heterogeneity of this RNA species is shown. Results point to redundancy for 5S RNA cistrons.

Isolation and characterization of a region of the Drosophila genome which contains a cluster of differentially expressed maternal genes (yema gene region)

We have characterized a genomic clone of Drosophila melanogaster which codes for four transcripts that are synthesized during oogenesis, remain abundant in the preblastoderm embryo, and then vanish during gastrulation. One of the transcripts varies in concentration along the anterior-posterior axis of the oocyte. This cluster of maternally acting genes (yema) maps to 98 F3-10 on chromosome arm 3 R.

Supragenic loop organization: mapping in Drosophila embryos, of scaffold-associated regions on a 800 kilobase DNA continuum cloned from the 14B-15B first chromosome region.

The supragenic loop organization of the Drosophila genome was investigated on a 800 kilobase (kb) DNA continuum from the 14B-15B first chromosome region. Nuclear scaffolds from 0-18 hr embryos were prepared with Laemmlis low-salt, detergent procedure and digested with restriction enzymes. Scaffold-associated regions (SARs) were mapped by probing Southern transfers of total, scaffold-associated and free DNA with a set of 70 recombinant phages overlapping the investigated genomic region. In all, 85 restriction fragments showed association to scaffolds. 12 of them were present in the majority of scaffolds. They bore strong SARs organizing the DNA molecule as consecutive loops with sizes ranging from 15 to 115 kb. 44 were present in only a fraction of scaffolds. They contained weak SARs subdividing the basic loops into smaller ones. 29 additional restriction fragments were present in a very small fraction of scaffolds. The position of SARs with respect to transcribed regions was investigated. Strong SARs appeared to be located on untranscribed DNA and to frame transcription units. In contrast, at least some weak SARs were shown to comap with transcribed regions or to reside within characterized transcription units. Statistical analyses established that strong and weak SARs were periodically positioned on the DNA continuum and that there was a potential contact point between scaffolds and the DNA continuum every 11 kb, or multiples thereof. Implications for SAR role(s) are discussed.

Localization of Some 5S RNA Cistrons on Escherichia coli Chromosome

Summary3 5S RNA cistrons, characterized by specific nucleotides sequences, are shown not to be linked.

A new ribosomal mutation which affects the two ribosomal subunits in Escherichia coli

SummaryA new ribosomal mutant resistant to erythromycin is described. The product of the gene eryC seems to be implicated in the assembly of the two ribosomal subunits, particularly in the maturation process of the RNA 23S and 16S.

Genetic and molecular analysis of terminal deletions of chromosome 3R of Drosophila melanogaster

Terminal deletions of chromosome 3R are induced at a high frequency (3.2 x 10(-3)) by irradiating 45-4 Drosophila melanogaster females with a low dose of X-rays. The 45-4 line carries a white transgene inserted at 16 kb from the terminus and is homozygous for the mu-2 mutation, a gene involved in the repair of double-strand DNA breaks. Four of the 51 recovered deleted strains have lost modulo, the distalmost essential gene on chromosome 3R. Breakpoints of 22 deletions have been localised in a single hybridisation step, using pulsed-field gel electrophoresis to separate genomic DNA fragments obtained from digestion with a rare-cutter restriction enzyme. Breaks do not occur at random, but are rather clustered in three susceptible chromosomal domains. Backcross experiments resulting in transheterozygous (deleted chromosome/45-4) animals indicate that the activity of the white transgene is enhanced when the DNA break has occurred proximal to a critical position. This suggests that homologous chromosomal pairing distal to the critical position results in the definition of a more compact chromatin structure and, due to position effect, in the silencing of white.

Assembly of Ribosomal Subunits Affected in a Ribosomal Mutant of E. coli Having an Altered L22 Protein

SummaryIn this article we describe some in vivo properties of a coldsensitive ribosomal mutant from Escherichia coli. The mutation affects the rplV gene which is the structural gene of ribosomal protein L22.Our work shows that at 22°C, the biosynthesis of both ribosomal subunits and the maturation processing of 16S and 23S ribosomal RNA are impaired. Integration of our results in a general model of in vivo ribosomal assembly in E. coli is presented.