The positive cofactor 4 (PC4) protein has an important role in transcriptional activation, which has been proposed to be mediated by transcription factor IIA (TFIIA) and TATA-binding protein-associated factors. To test this hypothesis, we cloned the Schizosaccharomyces pombe PC4 gene and analysed the role of the PC4 protein in the stimulation of basal transcription driven by TATA-containing and TATA-less promoters. Sc. pombe PC4 was able to stimulate basal transcription from several TATA-containing promoters and from the Initiator sequences of the highly transcribed Sc. pombe nmt1 gene. Moreover, it was demonstrated that Sc. pombe PC4 stimulates formation of the transcription preinitiation complex. Activation of transcription by PC4 was dependent on the Mediator complex and TFIIA, but was independent of TATA-binding protein-associated factor. PC4 binds to double-stranded and single-stranded DNA and interacts with TATA-binding protein, TFIIB, TFIIA, Mediator, TFIIH and the transcriptional activator protein VP16.