TY - STD TI - Proceedings of the National Academy of Sciences, [http://www.pnas.org] UR - http://www.pnas.org ID - ref1 ER - TY - STD TI - Cluster analysis and display of genome-wide expression patterns ID - ref2 ER - TY - STD TI - Selfish operons: horizontal transfer may drive the evolution of gene clusters. ID - ref3 ER -