Two low-molecular-weight nuclear RNA fractions were isolated from the loosely-bound non-histone proteins of calf thymus chromatin: RNA I (of 4 - 5.5S, heterogeneous on polyacrylamide-gel electrohoresis), and RNA IV (of about 3S). 2. Under the reinitiation conditions, RNA I stimulates about 2.5-fold the template properties of homologous chromatin with bacterial RNA polymerase, while RNA IV inhibits these properties by about 50%. 3. When reinitiation is blocked, RNA I stimulates both the initiation and elongation steps (by 20 - 30% and 60%, respectively). 4. The two RNA fractions equally inhibit transcription (by 30 - 35%) with free homologous DNA as a template.
