FIG. 4.—

Intron positions in the homeobox sequences of Arabidopsis thaliana. A consensus (majority) 60-residue homeodomain sequence is shown above a ruler where individual codon base positions are separated by tick marks. Intron positions are indicated by vertical lines labeled by the class names where each intron was found. The intron positions are generally conserved within each class. Exceptions are ATHB1, which has one intron, whereas other HD-ZIP I genes are single-exon genes; and At4g12750, a DDT class member, which has an extra intron at the beginning of the homeodomain. Gene classes not shown (HD-ZIP I, WOX, PLINC) do not have introns in the homeodomain. One of the splice sites in the NDX genes lies in the loop between helix 2 and helix 3 where it cannot be placed accurately on the consensus sequence. Its approximate position is marked by a crossbar at the end of the line.