Conversely, the insertion of either a scrambled sequence or the ISEm3 mutant sequence into this site did not facilitate splicing of the P7-generated pre-mRNA at the AAV5 donor site (Fig.3D, lanes 2 and 3). precursor mRNA (pre-mRNA), which is transcribed from a single promoter at map unit 6 (P6), through alternative splicing and polyadenylation (12). All the spliced B19V mRNA transcripts contain the central exon (exon 2), which spans the A1-1/A1-2 to D2 splice site (Fig.1). Therefore, splicing at the D2 donor site is a CCR4 antagonist 2 central step in control of B19V pre-mRNA processing. While analyzing the sequence of exon 2 with the program ESEfinder, CCR4 antagonist 2 version 3.0 (1,19) (Fig.2A), we found a number of SR protein-binding GAA motifs in exon 2 and a G/GU-rich region that lies directly 3 of the D2 donor site, which suggested that exonic splicing enhancers/intronic splicing enhancers (ESEs/ISEs) facilitate the definition of exon 2. SR proteins are serine/arginine-rich proteins that CCR4 antagonist 2 bind to ESEs/ISEs and function to promote exon inclusion during pre-mRNA processing (5,8). Identification of thecis-acting sequences that facilitate recognition of the D2 donor site will eventually reveal mechanisms that ensure CCR4 antagonist 2 appropriate expression levels of the capsid proteins VP1 and VP2, as well as the small nonstructural 11-kDa protein (11kDa), during B19V infection. == FIG. 1. == B19V transcripts and the probe used for RNase protection assays. Top, the B19V genome is depicted, with the locations of the terminal repeats (TR), the P6 promoter, the first intron donor (D1) and acceptor (A1-1 and A1-2) sites, the second intron donor (D2) and acceptor (A2-1 and A2-2) sites, the internal polyadenylation site (pAp), and the distal polyadenylation site (pAd) indicated. For each splice site, the nucleotide position is indicated. Middle, the antisense probe used in this study, probe 11, is shown with starting and ending nucleotides indicated (nt 2001 to 2560). Bands protected by this probe are diagramed, with their respective designations shown to the left and their length (in nucleotides) indicated to the right. More specifically, allUnspl represents all B19V mRNAs that are not spliced at any of the splice sites that lie between nt 2001 and 2560; SplA1-1/UnsplD2 and SplA1-2/UnsplD2 represent B19V mRNAs that are spliced at the A1-1 and A1-2 sites, respectively, but not at the D2 site; SplA1-1/SplD2 represents B19V mRNAs that are spliced from the A1-1 to D2 sites, and SplA1-2/SplD2 represents B19V mRNAs that are spliced from the A1-2 to the D2 sites. Bottom, the major transcripts (R1 to Rabbit Polyclonal to PLD1 (phospho-Thr147) R9) and the proteins they encode are shown, along with their lengths and molecular masses (in kilodaltons), respectively. Question marks indicate that proteins corresponding to these transcripts have not been identified or confirmed. All of the nucleotide numbers for the B19V genome that are used in this study refer to the B19V J35 isolate DNA CCR4 antagonist 2 with GenBank accession no.AY386330(24). == FIG. 2. == Exonic splicing enhancers (ESEs) in the central exon of the B19V genome. (A) Top, the B19V central exon (exon 2) is depicted, with the locations of splice sites and GAA motifs indicated. Middle, exon 2 sequence between the A1-1 and A1-2 sites (nt 2097 to 2203), with mutations in this region indicated (arrow plus nucleotide number) above the sequence, the identified ISE1 and ESE1 underlined, and mutant constructs tested in RNase protection assays identified and also shown below, in panel B. Bottom, exon 2 sequence between the A1-2 and D2 sites (nt 2222 to 2331), with mutations in this region indicated (arrow plus nucleotide number) above the sequence, identified ESE2 and ESE3 underlined, and mutant constructs tested in RNase protection assays identified and also shown below, in panel C. (B and C) RNase protection assays assessing the enhancer activities of the presence of ESE1 and ISE1 (B) and ESE2 and ESE3 (C). For these RNase protection assays, the C1NS1() plasmid and its mutation-containing derivatives (shown in panel A) were transfected into COS-7 cells. At 48 h posttransfection, total RNA was isolated and protected using probe 11. Transfections, RNA isolation, and RNase protection assays were performed as described previously (6,11,18). The protected bands are identified and labeled as the products described in the legend to Fig.1. The size maker was made as previously described (16). A representative protection assay from at least three independent experiments is shown. Ratios of SplA1-1 (SplA1-1/UnsplD2 + SplA1-1/SplD2) to allUnspl and of SplA1-2 (SplA1-2/UnsplD2 + SplA1-2/SplD2) to allUnspl are shown, respectively, for each protection assay; some are given as averages and standard deviations. == A GAA-rich sequence in the region between the A1-1 and A1-2 sites is essential for splicing at the A1-1 3 splice site. == We first generated a mutant.