AC19 subunit of Eukaryotic RNA polymerase (RNAP) I and RNAP III
The eukaryotic AC19 subunit of RNA polymerase (RNAP) I and RNAP III is involved in the assembly of RNAP subunits. RNAP is a large multi-subunit complex responsible for the synthesis of RNA. It is the principal enzyme of the transcription process, and is a final target in many regulatory pathways that control gene expression in all living cells. At least three distinct RNAP complexes are found in eukaryotic nuclei: RNAP I, RNAP II, and RNAP III. RNAP I is responsible for the synthesis of ribosomal RNA precursor, while RNAP III functions in the synthesis of 5S and tRNA. The AC19 subunit is the equivalent of the RPB11 subunit of RNAP II. The RPB11 subunit heterodimerizes with the RPB3 subunit, and together with RPB10 and RPB12, anchors the two largest subunits, RPB1 and RPB2, and stabilizes their association. The homology of AC19 to RPB11 suggests a similar function. The AC19 subunit is likely to associate with the RPB3 counterpart, AC40, to form a heterodimer, which stabilizes the association of the two largest subunits of RNAP I and RNAP III.
Comment:based on the structures of the multi-subunit complexes of yeast RNAP II and archaeal RNAP
Comment:The AC19/AC40 heterodimer of eukaryotic RNAP I and III is equivalent to the RPB11/RPB3 and L/D heterodimers of yeast RNAP II and archaeal RNAP, respectively.
Comment:The yeast RNAP II RPB11/RPB3 heterodimer (L/D heterodimer in archaea), together with RPB10 (N) and RPB12 (P), anchors the two largest subunits, RPB1 (A'/A") and RPB2 (B), stabilizing their association.