ABSTRACT

Higher organisms are composed of a myriad of tissues, each composed of cells differentiated to a specific state and function. Such cell differentiation is mediated by selective gene de-repression of an otherwise completely repressed genome, with the de-repressed genes being transcribed for specific ribonucleic acid (RNA) and protein synthesis characteristic of the differentiated state of that cell. Assays for de-repressor activity range between two major constraints: assays reflecting the biological role of the particular gene de-repression and assays reflecting the molecular uniqueness of the particular gene de-repression. De-repressor RNA offers several unique properties which favor its role in such a selective control mechanism. Certain species of low molecular weight nuclear RNA have been increasingly implicated as agents of specific gene de-repression in the cells of higher organisms and may play an important role in controlling gene expression during embryogenesis, cell differentiation, and the immune response.