Protein Domain : Nucleotidyltransferase, class I-like, C-terminal IPR011068

Type	Homologous_superfamily
Description	Nucleotidytransferases can be divided into two classes based on highly conserved features of the nucleotidyltransferase motif [ ]. Class I enzymes include eukaryotic poly(A) polymerase (PAP), archaeal tRNA CCA-adding enzyme and possibly DNA polymerase beta, while class II enzymes include eukaryotic and eubacterial tRNA CCA-adding enzymes. This superfamily represents the C-terminal domain of class I nucleotidyltransferases. The C-terminal domain has an alpha/beta sandwich fold, although the archaeal tRNA CCA-adding enzyme has a large insertion; this fold is reminiscent of the RNA-recognition motif fold. Poly(A) polymerase, the enzyme at the heart of the polyadenylation machinery, is a template-independent RNA polymerase that specifically incorporates ATP at the 3' end of mRNA. In eukaryotes, polyadenylation of pre-mRNA plays an essential role in the initiation step of protein synthesis, as well as in the export and stability of mRNAs. The catalytic domain of poly(A) polymerase shares substantial structural homology with other nucleotidyl transferases such as DNA polymerase beta and kanamycin transferase [ ]. The three invariant aspartates of the catalytic triad ligate two of the three active site metals. One of these metals also contacts the adenine ring. Furthermore, conserved, catalytically important residues contact the nucleotide. These contacts, taken together with metal coordination of the adenine base, provide a structural basis for ATP selection by poly(A) polymerase.The archaeal CCA-adding enzyme builds and repairs the 3 ' end of tRNA. A single active site (nucleotidyltransferase motif) adds both CTP and ATP [ ]. This enzyme is the only RNA polymerase that can build or rebuild a specific nucleic acid sequence without using a nucleic acid template.
Short Name	NuclTrfase_I-like_C