REBASE is a comprehensive database of information about restriction enzymes and related proteins. It contains published and unpublished references, recognition and cleavage sites, isoschizomers, commercial availability, methylation sensitivity, crystal and sequence data. DNA methyltransferases, homing endonucleases, nicking enzymes, specificity subunits and control proteins are also included. Most recently, putative DNA methyltransferases and restriction enzymes, as predicted from analysis of genomic sequences, are also listed. The data is distributed via Email, ftp (ftp.neb.com), and the Web (http://rebase.neb.com).