Polynucleotide Phosphorylase (PNPase) is a bifunctional enzyme with a phosphorolytic 3' to 5' exoribonuclease activity and a 3'-terminal oligonucleotidepolymerase activity. That is, it dismantles the RNA chain starting at the 3' end and working toward the 5' end. It also synthesizes long, highly heteropolymeric tails in vivo. It accounts for all of the observed residual polyadenylation in strains of Escherichia coli missing the normal polyadenylation enzyme. Discovered by Ochoa in 1951, the RNA-polymerization activity of PNPase was initially believed to be responsible for DNA-dependent synthesis of messenger RNA, a notion that got disproved by the late 1950s (http://www.jbc.org/content/281/15/e12.full.pdf).
Male and female animals underwent a standardized phenotypic screen to determine the effects of deletion. Twenty six tests were carried out on mutant mice and two significant abnormalities were observed. No homozygousmutant embryos were identified during gestation, and therefore none survived until weaning. The remaining tests were carried out on heterozygous mutant adult mice; no additional significant abnormalities were observed in these animals.
^ abcSymmons MF, Jones GH, Luisi BF (November 2000). "A duplicated fold is the structural basis for polynucleotide phosphorylase catalytic activity, processivity, and regulation". Structure8 (11): 1215–26. doi:10.1016/S0969-2126(00)00521-9. PMID11080643.