Characterization of the Like-U (LU) snRNA gene. (a) Genomic and genetic contexts of the LU snRNA locus. LU snRNA is encoded within the second intron of fas2; U5:23D is located in the third intron. PSEA/PSEB, proximal sequence element A/B (see Figure S7 in Additional file 1 for alignment of the U11 and LU promoters in Drosophilids). Locations of a P-element insertion and two deficiencies are indicated. The arrows on the deficiencies indicate that the regions extend beyond the displayed area. (b) Complementation analysis of LU snRNA mutations and deficiencies. Numbers of third instar larvae are indicated in parentheses. (c) Localization of LU snRNA in S2 cells determined by in situ hybridization using LU sense and antisense probes. (d) Predicted secondary structure of D. melanogaster LU snRNA. (e) Phylogeny of LU snRNA. (f) Alignment of Drosophilid LU snRNA orthologs using LocARNA. The blue box indicates the Sm site. Half-brackets indicate covariant base pairs.