TDP-43 is a highly conserved nuclear factor of yet unknown function that binds to ug-repeated sequences and is responsible for cystic fibrosis transmembrane conductance regulator exon 9 splicing inhibition. We have analyzed TDP-43 interactions with other splicing factors and identified the critical regions for the protein/protein recognition events that determine this biological function. We show here that the C-terminal region of TDP-43 is capable of binding directly to several proteins of the heterogeneous nuclear ribonucleoprotein (hnRNP) family with well known splicing inhibitory activity, in particular, hnRNP A2/B1 and hnRNP A1. Mutational analysis showed that TDP-43 proteins lacking the C-terminal region could not inhibit splicing probably because they were unable to form the hnRNP-rich complex involved in splicing inhibition. Finally, through splicing complex analysis, we show that splicing inhibition mediated by TDP-43 occurs at the earliest stages of spliceosomal assembly.In its most basic form, the splicing process has the task of removing from the primary RNA transcript all of those sequences (introns) that will not be present in the mature mRNA (1-3). Alternative splicing, i.e. the inclusion/exclusion of selected exonic sequences in particular tissues or developmental stages, has been heavily exploited by evolution to generate multiple mRNA transcripts from the same pre-mRNA sequence (4 -6). However, all of this flexibility also means that the splicing process is prone to mistakes following even minor changes (7), and alterations of splicing are being increasingly reported as the underlying cause of many genetic diseases (8 -12).At the molecular level, the removal of introns and the joining of exons are catalyzed by the spliceosome, which contains several hundred different proteins in addition to the five spliceosomal small nuclear RNAs (13,14). This complex arrangement of factors has two functions: first, to define the exact boundaries of an exon; and second, to catalyze the cut-and-paste generation of the mature mRNA. However, many external factors can also contribute to its workings, such as RNA secondary structure (15), transcription rates (16), the presence of splicing enhancer and silencer elements (17, 18), and even external stimuli (19,20). It is the combinatorial effect of all of these factors that will decide when, where, and to what degree a specific sequence will be included or not in the mature mRNA (17). Recently, the finding that at least 5% of all human alternative exons are derived from the highly repeated dimeric retrotransposons Alu elements has focused a lot of attention on the potential splicing modulatory ability of repeated nucleotide sequences (21).In previous works, we have focused our attention on clarifying the pathological role played by (ug)m-repeated sequences near the 3Ј-splice site of cystic fibrosis transmembrane conductance regulator (CFTR) 3 exon 9 (22-24), as they have been known to promote skipping and to correlate well with disease penetrance (25). In particular,...

The risk of sexual transmission of hepatitis C virus (HCV) infection was evaluated among 895 monogamous heterosexual partners of HCV chronically infected individuals in a long-term prospective study, which provided a follow-up period of 8,060 person-years. Seven hundred and seventy-six (86.7%) spouses were followed for 10 yr, corresponding to 7,760 person-years of observation. One hundred and nineteen (13.3%) spouses (69 whose infected partners cleared the virus following treatment and 50 who ended their relationship or were lost at follow-up) contributed an additional 300 person-years. All couples denied practicing anal intercourse or sex during menstruation, as well as condom use. The average weekly rate of sexual intercourse was 1.8. Three HCV infections were observed during follow-up corresponding to an incidence rate of 0.37 per 1,000 person-years. However, the infecting HCV genotype in one spouse (2a) was different from that of the partner (1b), clearly excluding sexual transmission. The remaining two couples had concordant genotypes, but sequence analysis of the NS5b region of the HCV genome, coupled with phylogenetic analysis showed that the corresponding partners carried different viral isolates, again excluding the possibility of intraspousal transmission of HCV. Our data indicate that the risk of sexual transmission of HCV within heterosexual monogamous couples is extremely low or even null. No general recommendations for condom use seem required for individuals in monogamous partnerships with HCV-infected partners.