We have characterized a novel transcriptional activity from HeLa cells that is required for ribosomal gene transcription by RNA polymerase I. This activity has a native molecular mass of 16 kDa and does not bind to conventional chromatographic resins. Single-round and immobilized-template experiments revealed that initiation complex formation is independent of the novel activity. Functional studies showed that it stimulates the transition from initiation to elongation, promoter escape. Thus the novel activity does not resemble the mouse initiation/elongation factor TIF-IC but is a true novel entity. (C) 2009 Elsevier Inc. All rights reserved.