General information on PAPD5 Human Protein
PAPD5 protein is a member of non-canonical poly(a) polymerases also known as Cidl1-like proteins. Non-canonical poly(A) polymerases are very similar to canonical poly(a) polymerases but have different nucleotide-base recognition motif. The latter are responsible for the addition of a poly(A) tail to the 3’ end by poly(A) polymerases to mRNAs which leads to their degradation. Non canonical PAPs, such as PAPD5 protein, are responsible for the cytoplasmic polyadenylation of mRNAs and polyadenylation mediated degradation of RNAs. Other members of this family of proteins may also be involved in the addition of uridyl residues of RNAs.
Human PAPD5 protein is involved in the polyadenylation-mediated degradation of aberrant pre-rRNAs. This protein has also been reported to be involved in the degradation of replication-dependent histone mRNAs. These mRNAs do not have a poly(A) tail but end in a stem-loop structure. In this case, the degradation pathway starts with PAPD5 protein adding a poly(U) tail which is recognized by the Lsm1-7 complex. This recognition leads to decapping and degradation of the mRNAs. Other functions of PAPD5 protein include DNA binding, DNA-directed DNA polymerase activity, guanylyltransferase activity, metal ion binding, polynucleotide adenylyltransferase activity, RNA binding, telomerase RNA binding. PAPD5 protein is involved in cell division, cell cycle carbohydrate homeostasis and other biological processes.
PAPD5 protein is believed to act as a kind of scavenger enzyme for aberrant RNAs which, due to misfolding and misprocessing, cannot form the correct interactions. This function is similar to the role of TRAMP4 complex in yeast. Like the latter, PAPD5 protein can be found in nucleus which suggests that the protein may be part of a nuclear surveillance machinery. The downregulation of PAPD5 may not lead to a significant change in RNA level. This seems to suggest that the RNA surveillance system is most likely reductant, making sure that deleterious aberrant RNAs are degraded with high efficiency.
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