snRNA-activating protein complex subunit 5 (also known as SNAPC5 or SNAPc19) is part of the core components of the SNAPc complex required for the transcription of both RNA polymerase II and III small-nuclear RNA genes []. The RNA polymerase II snRNA promoters consist of a proximal sequence element (PSE), while the RNA polymerase III snRNA promoters consist of both a PSE and a TATA box. SNAPc binds to the PSE in both RNA polymerases and other PSE sequences in other snRNA genes. Therefore, SNAPc is also called the PSE transcription factor (PTF) or PSE-binding protein (PBP). The human SNAPc19 and SNAPc45 subunits are dispensable for transcription in vitro and are not as widely conserved as the other three, SNAPc190, SNAPc43 and SNAPc50, suggesting that these vertebrate-specific SNAPc subunits may have adapted specialised regulatory roles for snRNA gene transcription [].
