The SIII (or elongin) transcription elongation factor complex stimulates the rate of transcription elongation by RNA polymerase II by suppressing the transient pausing of the polymerase at many sites along the DNA template. This complex is a heterotrimer, composed of the transcriptionally active subunit A, A2 or A3 (or elongin A, A2 or A3) and two regulatory subunits, B and C (or elongin B and C). This gene encodes subunit A3. A3 and A are ubiquitously expressed, whereas A2 is specifically expressed in the testis. [provided by RefSeq, Mar 2010].