Bioinformatics analysis of the relationships between Alu and its downstream miRNA genes. A. Schematic diagram of the structural relationships of Alu elements, miRNA genes and other sequences, suggesting that some miRNAs downstream of Alu elements may be transcribed by Pol-III through an Alu sequence. B. The length distribution of Alu transposons through which miRNAs may be transcribed. The X axis is the Alu transposon length and the Y axis is the number of Alu sequences. C. Alu sequences upstream of miRNA genes are divided into two groups: m200, longer than 200 bp; and l200, shorter than 200 bp. The ATGC content was determined by extracting sequences in line with the A and B boxes from the multiple sequence alignment results. The height of each letter is proportional to the frequency of the nucleotide indicated. Solid letters correspond to the position relative to the starting point of the A or B box. D. The distribution of Alu sequences followed by miRNA genes in the human genome. The abscissa is the location of Alu and miRNA genes: inter = sequences between protein-coding genes, anti = antisense strands of genes and intron = introns. The ordinate indicates the number of sequences.