Sub1/PC4 a chromatin associated protein with multiple functions in transcription

Yeast Sub1 and its human ortholog PC4 display multiple cellular functions in vivo. Sub1/PC4 contains a unique conserved non-specific DNA-binding domain and is involved in distinct DNA-dependent processes including replication, DNA repair and transcription. Sub1/PC4 is a non-histone chromatin-associated protein initially described as a co-activator for RNA polymerase (Pol) II transcription in vitro. Recently, biochemical and genomic studies showed that Sub1 is not restricted to Pol II transcription but is also involved in Pol III transcription revealing a more general role in transcription than anticipated. Sub1/PC4 appears to play a dual (positive and negative) complex role in gene expression and has multiple effects in distinct steps of the transcription cycle, consisting of initiation, elongation, termination and reinitiation. Here, the multiple transcriptional functions of Sub1/PC4 will be reviewed and the recent findings and their possible implications in the understanding of Sub1/PC4 function in transcription will be discussed.