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. 2018 Jul 24;2(2):161–173.

Figure 1.

Figure 1

A. Genomic organization of the chicken U4X and U4B snRNA genes. The genes are transcribed left-to-right, as indicated by the arrows. Cross-hatched boxes indicate the locations of the enhancer (Enh) and proximal sequence elements (PSE) conserved in the 5′ flanking DNA of vertebrate snRNA genes. B. Similarities and differences in the promoters of the chicken U4B, U4X, and U1 snRNA genes. The schematic diagram shows the locations of the PSE and of the octamer and SPH motifs that are conserved at nearly identical positions upstream of the U4B, U4X, and U1 genes. The sequence comparisons at the bottom of the figure show that among these three genes the regulatory motifs are quite similar but not identical in sequence. Underlines point out nucleotides in the octamer, SPH, and PSE motifs that are different in one sequence but conserved in the other two. The double-ended arrow indicates the location of a palindromic sequence unique to the U4X gene that partially overlaps the U4X PSE. The U1 sequences shown are from the Ul-52a gene (Earley et al., 1984). The U1 gene octamer and SPH motifs occur naturally in the opposite orientation compared to those in the U4 genes; therefore the U1 octamer and SPH motif sequences shown in the figure are from the template strand, whereas all other sequences are from the non-template strands.