Component of the PAF1 complex (PAF1C) which has multiple functions during transcription by RNA polymerase II (By similarity). PAF1C associates with RNA polymerase II, is involved in transcriptional elongation and in histone modifications including methylation on histone H3 'Lys-4' (H3K4me3) (By similarity). Component of the PAF1 complex, which at least consists of cdc73, paf1, leo1, ctr9 and rtf1 (By similarity). The PAF1 complex interacts with PHF5A (By similarity).