The PAF1 complex is a multifunctional complex. Involved in transcription initiation via genetic interactions with TATA-binding proteins. Involved in elongation. It regulates 3'-end formation of snR47 by modulating the recruitment or stable association of NRD1 and NAB3 with RNA polymerase II. Also has a role in transcription-coupled histone modification. Required for activation of RAD6 ubiquitin conjugate and the BRE1 ubiquitin ligase which ubiquitinate 'Lys-126' histone H2B. Activates the SET1 histone methyltransferase complex for methylation of 'Lys-4' of histone H3 and for methylation of 'Lys-73' of histone H3 by DOT1 and 'Lys-36' of histone H3 by SET2. Component of the PAF1 complex which consists of at least CDC73, CTR9, LEO1, PAF1 and RTF1. Interacts with FACT subunits POB3 and SPT16. Belongs to the CDC73 family.