There are several RNA silencing pathways that are variations on the basic mechanism described above. One approach to understanding this diversity is through the Argonaute proteins. In Arabidopsis there is a ten member multigene family for Argonaute proteins and we are investigating their expression patterns, mutant phenotypes and the characteristics of bound short RNAs. The emerging picture is that Argonaute targets different types on longer RNA because they are not all associated with the same type of 21-25nt RNA. This diversity of Argonaute proteins allows RNA silencing to have many different effects on genetic regulation.