Poly A polymerase, head domain (IPR002646)

Short name: PolA_pol_head_dom

Overlapping homologous superfamilies


Domain relationships



This group includes nucleic acid independent RNA polymerases, such as polynucleotide adenylyltransferase (EC:, which adds the poly (A) tail to mRNA. This group also includes the tRNA nucleotidyltransferase that adds the CCA to the 3' of the tRNA (EC:

CCA-adding enzymes add the sequence [cytidine(C)-cytidine-adenosine (A)]., one nucleotide at a time, onto the 3' end of tRNA, in a template-independent reaction [PMID: 16171400, PMID: 16364630]. This Class II group is comprised mainly of eubacterial and eukaryotic enzymes and includes Bacillus stearothermophilus CCAase [PMID: 12526808], Escherichia coli poly(A) polymerase I [PMID: 15737627, PMID: 10594833], human mitochondrial CCAase [PMID: 12729736, PMID: 11504732], and Saccharomyces cerevisiae CCAase (CCA1) [PMID: 2204621, PMID: 1448105, PMID: 1634528]. CCA-adding enzymes have a single catalytic pocket, which recognizes both ATP and CTP substrates [PMID: 10361280, PMID: 10666455]. This family belongs to the Pol beta-like NT superfamily [PMID: 10075991, PMID: 7482698].

Escherichia coli CCAase is related to this group but has not been included in this alignment as this enzyme lacks the N-terminal helix conserved in the remainder of the NT superfamily.

In the Pol beta-like NT superfamily [PMID: 10075991, PMID: 7482698], the majority of enzymes have two carboxylates, Dx[D/E], together with a third more distal carboxylate, which coordinate two divalent metal cations involved in a two-metal ion mechanism of nucleotide addition. These carboxylate residues are fairly well conserved in this family.

GO terms

Biological Process

GO:0006396 RNA processing

Molecular Function

GO:0003723 RNA binding
GO:0016779 nucleotidyltransferase activity

Cellular Component

No terms assigned in this category.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.