Search

Although parvoviruses are found throughout the animal kingdom, only the human pathogenic B19 virus has so far been shown to possess a limited host range, with erythroid progenitor cells as the main target cells supporting B19 propagation. The underlying mechanism of such erythroid tropism is still unexplained. Synthesis of the NS1 nonstructural protein occurs in permissive and nonpermissive cells, such as megakaryocytes, whereas synthesis of the VP1 and VP2 capsid proteins seems to be restricted to burst-forming units and CFU of erythroid cells. In nonpermissive cells, the NS1 protein is overexpressed and the NS1 RNAs are the predominant RNA species. However, the VP1 and VP2 proteins are not detectable, although the corresponding mRNAs are synthesized. Since all transcripts have part of the 5' untranslated region (5' UTR) in common but distinct 3' UTRs characterizing the nonstructural- and structural-protein mRNAs, we investigated, in transient transfection assays, the possible involvement of the 3' UTR of the capsid protein mRNAs in VP1 and VP2 protein synthesis in nonpermissive Cos cells. The results showed that (i) the 3' UTR of mRNAs coding for the capsid proteins repressed VP1 and VP2 protein synthesis, (ii) the 3' UTR did not affect nuclear export or mRNA stability, and (iii) mRNAs bearing the 3' UTR of the capsid protein mRNAs did not associate with ribosomes at all. Taken together, these results indicate that in nonpermissive cells, the 3' UTR of the capsid protein mRNAs represses capsid protein synthesis at the translational level by inhibiting ribosome loading.

The major tRNA genes in S. cerevisiae mitochondria are contained within a 20 kb segment of the mitochondrial DNA. In order to analyze the functional role of this region we have isolated several mitochondrial mutations, which are temperature-sensitive for growth on non-fermentable carbon sources. These mutations, localized in the major tRNA cluster region, can be classified in different groups according to their (a) genetic and physical localization, (b) spectrum of suppression and (c) biochemical characteristics. Some of these are mutations in tRNA genes which affect tRNA function; others alter the synthesis of the gene product. Finally, we found two mutations localized in, or in the vicinity of, the open reading frame RF2. RF2 has been postulated to be a maturase-like protein (Michel 1984) but no function for it has yet been demonstrated. The existence of defective mutants may confirm that RF2 is indeed necessary for mitochondrial biogenesis and so allow for a study of the expression of this gene.

The role of the syllable during on-line speech perception was explored using a variant of the phoneme detection task developed by Pitt and Samuel (1990). In their task, listeners' attention to phonemes in different serial positions inside word or nonword stimuli was manipulated by varying the probability that a target phoneme occurred in the various positions. In our experiments, French and Spanish subjects had to detect targets that appeared either in the coda of the first syllable or in the onset of the second syllable of carrier words. Subjects' expectations about the structural position of the target were manipulated. In a series of five experiments (two using a decision paradigm and three using a detection paradigm), these expectations were shown to influence response latencies: that is, subjects who attended to the coda of the first syllable were faster when the target appeared in this position rather than in the onset of the second syllable; the reverse pattern was observed when subjects attended to the onset of the second syllable. This result held regardless of the serial position of the target. These results were equally valid for French and Spanish. Moreover, syllabification was present when Spanish pseudowords were used as carriers. The fact that subjects could focus their attention on a syllabically defined position, even when processing nonwords, suggests that syllabic information is specified at a prelexical level of representation. The phoneme detection task in which attention is manipulated provides us with an interesting new technique for exploring prelexical representations.Copyright 1993, 1999 Academic Press

Human parvovirus B19 recombinant VP1 and VP2 capsid proteins were produced by a procaryotic pGEX expression plasmid to evaluate the humoral response by immunoblot assay in 14 patients with primary infection. The same concentrations of VP1 and VP2 recombinant proteins were used. This demonstrates that VP1 immunoglobulin M detection and/or VP1 immunoglobulin G seroconversion is a reliable marker of primary infections. Consequently, detection of antibodies to B19 VP1 might be helpful for identifying patients at risk for chronic B19 infection or patients who are susceptible to viral reinfection.