Sequence and analysis of chromosome 3 of the plant Arabidopsis thaliana

Arabidopsis thaliana is an important model system for plant biologists(1). In 1996 an international collaboration (the Arabidopsis Genome Initiative) was formed to sequence the whole genome of Arabidopsis(2) and in 1999 the s equence of the first two chromosomes was reported(3,4). The sequence of the last three chromosomes and an analysis of the whole genome are reported in this issue(5-7). Here we present the sequence of chromosome 3, organized i nto four sequence segments (contigs). The two largest (13.5 and 9.2 Mb) cor respond to the top (long) and the bottom (short) arms of chromosome 3, and the two small contigs are located in the genetically defined centromere(8). This chromosome encodes 5,220 of the roughly 25,500 predicted protein-codi ng genes in the genome. About 20% of the predicted proteins have significan t homology to proteins in eukaryotic genomes for which the complete sequenc e is available, pointing to important conserved cellular functions among eu karyotes.