Center for Biological Sequence Analysis, BioCentrum-DTU, Building 208, The Technical University of Denmark, DK-2800 Lyngby, Denmark. ljj@cbs.dtu.dk|Center for Biological Sequence Analysis, BioCentrum-DTU, Building 208, The Technical University of Denmark, DK-2800 Lyngby, Denmark. ljj@cbs.dtu.dk|Center for Biological Sequence Analysis, BioCentrum-DTU, Building 208, The Technical University of Denmark, DK-2800 Lyngby, Denmark. ljj@cbs.dtu.dk|Center for Biological Sequence Analysis, BioCentrum-DTU, Building 208, The Technical University of Denmark, DK-2800 Lyngby, Denmark. ljj@cbs.dtu.dk