F. Gigliani

The HIV Tat protein affects processing of ribosomal RNA precursor

BackgroundInside the cell, the HIV Tat protein is mainly found in the nucleus and nucleolus. The nucleolus, the site of ribosome biogenesis, is a highly organized, non-membrane-bound sub-compartment where proteins with a high affinity for nucleolar components are found. While it is well known that Tat accumulates in the nucleolus via a specific nucleolar targeting sequence, its function in this compartment it still unknown.ResultsTo clarify the significance of the Tat nucleolar localization, we induced the expression of the protein during oogenesis in Drosophila melanogaster strain transgenic for HIV-tat gene. Here we show that Tat localizes in the nucleoli of Drosophila oocyte nurse cells, where it specifically co-localizes with fibrillarin. Tat expression is accompanied by a significant decrease of cytoplasmic ribosomes, which is apparently related to an impairment of ribosomal rRNA precursor processing. Such an event is accounted for by the interaction of Tat with fibrillarin and U3 snoRNA, which are both required for pre-rRNA maturation.ConclusionOur data contribute to understanding the function of Tat in the nucleolus, where ribosomal RNA synthesis and cell cycle control take place. The impairment of nucleolar pre-rRNA maturation through the interaction of Tat with fibrillarin-U3snoRNA complex suggests a process by which the virus modulates host response, thus contributing to apoptosis and protein shut-off in HIV-uninfected cells.

pR plasmid replication provides evidence that single-stranded DNA induces the SOS system in vivo

Evidence is presented that the pR bat gene is essential for plasmid replication and for spontaneous induction of the SOS response in Escherichia coli. Mutations preventing single-stranded DNA production, needed for pR plasmid replication, also prevent the induction of the SOS system. The following experimental design was used. Firstly, we identified the minima rep region, defined as the minimal DNA sequence necessary for pR plasmid replication and, secondly, analyzed the nucleotide sequence of this region. This identified structures and functions (ori-plus, on-minus and Rep protein) homologous to those found in phages and plasmids replicating by the rolling-circle mechanism. Finally, mutations were introduced either in the replication protein catalytic site or in the nick site consensus sequence, which caused the pR plasmid to lose its ability to induce the SOS system. We conclude that, in this system, the in vivo SOS-inducing signal appears to be the single-stranded DNA produced during pR replication.

Interactions among the bHLH domains of the proteins encoded by theEnhancer of split andachaete-scute gene complexes ofDrosophila

TheEnhancer of split andachaete-scute gene complexes [E(spl)-C and AS-C] encode helix-loop-helix proteins required for neurogenesis inDrosophila. Using a heterologous bacterial system, we show that (i) the bHLH domains of the proteins encoded by the two gene complexes differ in their ability to form homo- and/or heterodimers; (ii) the bHLH domains of the E(spl)-C proteins m5, m7 and m8 interact with the bHLH domains of the Ac and Sc proteins. These bHLH domains form an interaction network which may represent the molecular mechanism whereby the competent state of the proneural cells is maintained until the terminal determination to neuroblast occurs. Also, the pattern of interactions of the bHLH domains of certain proteins encoded by the two gene complexes may explain their functional redundancy.

Frequency of satellite association in individuals with structural abnormalities of nucleolus organiser region

SummaryThe frequency of involvement of acrocentric chromosomes into satellite association has been extensively studied in recent years. These studies have aimed to show the existence of a relationship between satellite association, centric fusion and non-disjunction. In the present paper, evidence is given that different D-group chromosomes all bearing structural abnormalities in the nucleolus organizer region are preferentially involved in satellite association. Some interpretations of this finding are discussed.ZusammenfassungDie Häufigkeit der Beteiligung akrozentrischer Chromosomen bei Satellitenassoziation ist in den letzten Jahren eingehend untersucht worden. Diese Untersuchungen hatten zum Ziel, die Beziehungen zwischen Satellitenassoziation, zentrischer Fusion und Non-disjunction aufzuzeigen. Hier könnte dargelegt werden, daß verschiedene D-Chromosomen, die einen Defekt in der Region des Nucleolus-Organisators haben, bevorzugt an der Satellitenassoziation beteiligt sind. Erklärungen dieser Befunde werden diskutiert.

Double satellites: Autoradiographic study of a chromosomal marker observed in two generations

Summary2 cases of a familial balanced translocation of satellites and part of the short arm between two D-group chromosomes are described.One of these chromosomes shows double satellites on its short arm, and the other appears deprived of visible satellites and part of its short arm. These chromosomes have been identified by means of autoradiography as a number 15 and a number 14, respectively.The possible implications of this type of translocation are discussed in the text.ZusammenfassungEs wird bei Tochter und Mutter eine balancierte Translokation von Satelliten und einem Teil des kurzen Arms zwischen zwei D-Chromosomen beschrieben.Eines dieser Chromosomen zeigt doppelte Satelliten an seinem kurzen Arm, bei dem anderen ist ein Satellit nicht zu erkennen, und es scheint ein Teil des kurzen Arms zu fehlen. Mit Hilfe der Autoradiographie ist jenes als Nr. 15, dieses als Nr. 14 charakterisiert.Die mögliche Bedeutung dieses Typs von Translokation wird besprochen.

A marker chromosome number 14 with double satellite observed in two generations: An unbalanced chromosome constitution associated with normal phenotype

Summary2 phenotypically normal subjects, both carriers of a double satellite on the short arm of a D-group chromosome, have been studied. The marker chromosome has been identified as a number 14 by means of autoradiography. All D-and G-group chromosomes show satellites in both subjects. Two of the possible mechanisms of formation of a double satellite are described. The variability in the expression of satellites and the frequency of satellite association of the single D-group chromosomes have also been studied. It has to be stressed that these individuals, though being carriers of a partial trisomy, are both phenotypically normal.Zusammenfassung2 phänotypisch normale Personen, die beide Träger von doppelten Satelliten eines kurzen Arms der D-Gruppe sind, wurden untersucht. Das Markierungschromosom wurde autoradiographisch als Nr. 14 identifiziert. Alle D-und G-Chromosomen zeigen bei beiden Personen Satelliten. Zwei mögliche Mechanismen der Bildung von doppelten Satelliten werden beschrieben. Die Variabilität des Vorkommens von Satelliten und die Häufigkeit der Satellitenassoziation von einzelnen D-Chromosomen wurden untersucht. Es wird darauf hingewiesen, daß diese Personen als Träger einer partiellen Trisomie beide phänotypisch normal sind.

Red Cell Phosphoglucomutase Polymorphism; I. Enzyme Activity of Different Red Cell PGM Phenotypes

The red cell PGM activities have been determined in 95 individuals with PGM11 phenotype, in 86 with PGM12–1 and in 18 with PGM12 phenotype. The average activities of t

Partial deletion of the X chromosome in gonadal dysgenesis 46,X,del(X)(p22) identified by BudR treatment.

SummaryIn this report we describe a deletion of the short arm of the X chromosome in a 16-year-old female with gonadal dysgenesis.The breakpoint was localized by BUdR treatment and acridine orange staining in region 2, band 2.Of the examined cells, 3% showed an early replication of the deleted X chromosome.

Gene frequencies of adenylatekinase polymorphism in the Roman population

SummaryThe red cell AK phenotypes of 841 hemolysates from unrelated individuals living in Rome have been determined by the starch gel electrophoretic method of Fildes and Harris (1966). The observed gene frequencies were: AK1=96.3 and AK2=3.7.

Red cell phosphoglucomutase polymorphism. II. Densitometric studies.

The relative activities associated with the different electrophoretic PGM bands have been measured by a densitometric method in hemolysates from 53 PGM1 1, 3 8 PGM1 2–1 and 8 PGM1 2 individuals. The mean PGM1 relative activity was the same in the three PGMt phenotypes, which also have the same total mean PGM activity. It seems, therefore, that the two common PGM1 alleles have the same associated enzymatic activity.